tony nankervis on thu 25 apr 96
Rick
For what its worth - I solved a pinholing problem several years ago by
replacing the rutile in a glaze with titanium. - cheers
Tony Nankervis
Ceramics Dept
Visual Arts
Southern Cross University
Lismore 2480 NSW Australia
Hanne Bjorklund on fri 26 mar 99
Hi Niels
One of the best pieces of advice I have ever been given was to wipe every
piece of bisque ware with a damp cloth or sponge just before glazing.
Invisible dust particles can cause pinholes. There are several other causes
of pinholes, and someone more clever than I can explain how to tell the
difference. (It has to do with the edge of the pinhole.) My glazing 'room'
is under my pole house on a hillside. There is a roof, (my house) but no
walls,
a dirt floor and lots of fresh air, and I am sure that everything has some
dust on it whether
I can see it or not. I have come to like the ritual of preparing each pot
(mainly large platters) for the glaze, but I don't know how I would feel
about wiping dozens of smaller pieces. However, post firing pinholes do not
happen.
Hanne
bjorklund@clear.net.nz
Stanley Irvin on fri 17 sep 99
Ron,
Your message to Joan mentioned "calclation". Could you say more about what
this is?
Ron Roy on sat 18 sep 99
It's my spelling again - that word should be calculation of course.
Stanley - if this is not the amswer you were looking for ask again and
brace yourself - there are quite a few on this list that just love to
explain the virtues of glaze calculation.
RR
>----------------------------Original message----------------------------
>Ron,
>Your message to Joan mentioned "calclation". Could you say more about what
>this is?
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Cindy Strnad, Earthen Vessels Pottery on sun 19 sep 99
Stanley,
These factors have likely been mentioned, but I didn't see if they were.
Aside from adjusting your glaze, you can try:
*Bisque fire to ^04 and soak for an hour
*Make certain your bisque is not dusty. It can be dusty from the kiln, BTW.
Vacuum your kiln regularly. If needed, sponge pots off with damp
sponge/cloth or else just wash them and wait until they're dry before
glazing. If you have an outdoor place to do this, you can blow the dust off
with a blast from the air compressor.
*Soak your glaze load and/or bring up to final temperature very slowly. Be
certain not to over-fire, though.
None of these things will help if your glaze needs reformulating, but
they're worth looking at.
Cindy Strnad
Earthen Vessels Pottery
Custer, SD
Virgil and Susan Leise on wed 12 apr 00
------------------
Hi, I want to thank everyone for all the suggestions concerning the pinhole
problem I was having=21=21 I really think that it is something in the clay.=
I will
do another test tho..and try soaking the bisque....one more time=21 I do =
fire the
bisque at 04 and the glaze at 6 in an electric kiln. I do most of the =
things
that everyone suggested already.
I really appreciate the article on simple tests..by Tom Buck..thanks for =
taking
the time to send that info=21=21
After this test...I think I will probly order clay from another place..and =
try
that. I don't do this for my living..but really enjoy making pots and =
selling
what I do make...it is really discouraging to have a problem=21
Thanks again
Susan (in Nebr)
Veena Raghavan on thu 13 apr 00
Message text written by Ceramic Arts Discussion List
>After this test...I think I will probly order clay from another place<
Hi Susan,
I think your decision to order other clay is probably a good one.
At the studio where I do my work, they provide a cone 6 buff stoneware, and
for quite some time there has been a pinholing problem. The bisque is 04
and the glaze is 6, so that is not the problem. I also use some of my own
clays, P-5 porcelain from Highwater, and a red/brown cone 6-8 stoneware
from Standard, and the pinholing does not occur on either of these clays,
even when I use the same glazes. Thus, I feel it is the buff stoneware clay
that is causing the pinholes.
Good luck with locating a new clay which works for you.
All the best.
Veena
Veena Raghavan
75124.2520@compuserve.com
mel jacobson on wed 14 nov 01
mr. uchida would say. `one pinhole on a pure white pot
looks like a big pimple on the nose of a girl going to a dance.`
also,`ten pinholes on a farmer art pot does not matter`.
also, `one pinhole on a ming celedon vase is awful.`
also, `50 pinholes on melsan's minnesota pots would
not matter at all.` (rhodes 32 with heavy iron spotting)
so, the bottom line is:
depends on the pot and glaze and the claybody...and of course, on the
aesthetic of the potter. i am rarely upset with pinholes. a part
of my work. they do not really show at all. but, then, at cone 11
glazes do not naturally pinhole, the glaze seals up really well.
clear, light colored cone 6 glazes will show pinholes as bad flaws.
so, get them to fit right. it does take work you know.
and listen to ron roy about bisque firing. slow down...take 12 hours
or more. slow down....it costs nothing to bisque slow....it is the
amps you use, not the time.
mel
time for hunting, no snow, 65 on friday. have to sit in the deer
stand with a cooler of soft drinks. ice. sweat in a deer stand.
geez.
but, just wait, the winter is coming. the hawk is going to be back
with a fury. minnesota people know.
From:
Minnetonka, Minnesota, U.S.A.
web site: http://www.pclink.com/melpots
Lisa Williams on sun 28 jul 02
Hi all!
Here is another silly question from the peanut gallery! I am getting
pinholes in my ^6 glazes that I am painting on. They are teeny-tiny. I am
having trouble with the texture spectrum glazes - (I am not ready to make my
own yet - that is my goal for next year). Any glaze (opulence) that I dip is
fine and any glaze that is not a texture (spectrum, campbell's) is not
pinholing. I bisque to ^06 and am using Highwater Brownstone clay.
I know I am putting the glaze on too thick, but when I try to thin it out it
looks really yucky.....how do you know when it is "just right"?
The big question is: Do the pinholes make the glaze not foodsafe? Do I
trash the pots?
Thanks for any input!
Lisa Williams in muggy NC
Ron Roy on tue 30 jul 02
Hi Lisa,
Stoneware clays usually have more carbonous material in them so they need a
clean bisque firing - lots of oxygen to help burn that stuff out - and
perhaps a slower firing from 700C to 900C - and maybe a higher bisque to
04.
If the pin holes are small you may be able to eliminate them buy a soaking
period it the end of you glaze firing - try a 15 min. soak and/or a slow
cool - like leaving your switches on medium after the cone is down - say
for 30 min. Gives the pin holes a chance to heal over.
If a glaze is unstable when in contact with food pin holes will make the
problem worse because the pinholes give a greater surface for acids to work
on.
If the glaze is stable then the pinholes don't make a difference except to
clean ability.
RR
>Hi all!
>
>Here is another silly question from the peanut gallery! I am getting
>pinholes in my ^6 glazes that I am painting on. They are teeny-tiny. I am
>having trouble with the texture spectrum glazes - (I am not ready to make my
>own yet - that is my goal for next year). Any glaze (opulence) that I dip is
>fine and any glaze that is not a texture (spectrum, campbell's) is not
>pinholing. I bisque to ^06 and am using Highwater Brownstone clay.
>
>I know I am putting the glaze on too thick, but when I try to thin it out it
>looks really yucky.....how do you know when it is "just right"?
>
>The big question is: Do the pinholes make the glaze not foodsafe? Do I
>trash the pots?
>
>Thanks for any input!
>
>Lisa Williams in muggy NC
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Christena Schafale on tue 30 jul 02
Lisa,
I suspect, though I don't know for sure, that the Spectrum "texture" glazes
contain a lot of rutile to create the texture effect, and rutile is said to
cause pinholing. I would guess that might be why you are having the
problem with them and not with your other glazes. As to what you can do --
if you find out, let me know, since I also have this problem with high
rutile glazes, even with soaking and slow cooling.
Chris
> >Hi all!
> >
> >Here is another silly question from the peanut gallery! I am getting
> >pinholes in my ^6 glazes that I am painting on. They are teeny-tiny. I am
> >having trouble with the texture spectrum glazes - (I am not ready to make my
> >own yet - that is my goal for next year). Any glaze (opulence) that I
> dip is
> >fine and any glaze that is not a texture (spectrum, campbell's) is not
> >pinholing. I bisque to ^06 and am using Highwater Brownstone clay.
> >
> >I know I am putting the glaze on too thick, but when I try to thin it out it
> >looks really yucky.....how do you know when it is "just right"?
> >
> >The big question is: Do the pinholes make the glaze not foodsafe? Do I
> >trash the pots?
> >
> >Thanks for any input!
> >
> >Lisa Williams in muggy NC
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>Fax: 613-475-3513
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
Consultation and Referral Specialist
Resources for Seniors
christenas@rfsnc.org
http://www.resourcesforseniors.com
Phone: (919) 713-1537
FAX: (919) 872-9574
1110 Navaho Dr, Suite 400
Raleigh, NC 27609
Ian Currie on wed 31 jul 02
Hi Chris
Wish I could offer some magic solution to the problem of rutile and
titanium dioxide causing pinholing. But as it is one of those perennial
problems I'm pleased to see you putting it to Clayart. If one is lucky,
a grid around the glaze you are using (grid method for those who have
not heard of it... see my website below)... a grid will *sometimes*
reveal a similar glaze with no pinholing. I have evidence on some grids
that the titanium-caused pinholes are in a zone between the more fluid
glazes where the pinholes may smooth over (not always!!) and stiff
glazes, for example the high alumina glazes, where the micro-pores in
the glaze have not started to move yet to ptoduce visible bubbles.
Apart from this I have not found any consistent thing that seems to
promote or retard this sort of pinhole. Help someone??
Just repeating something I mentioned in a previous e-mail some months
ago regarding pinholing... some iron-bearing dark clays seem to
chronically cause pinholing at midfire (^5 or 6) in oxidation. Here the
usual remedy is to change clays.
Cheers
Ian
http://ian.currie.to/
Christena Schafale wrote:
> Lisa,
>
> I suspect, though I don't know for sure, that the Spectrum "texture"
> glazes
> contain a lot of rutile to create the texture effect, and rutile is
> said to
> cause pinholing. I would guess that might be why you are having the
> problem with them and not with your other glazes. As to what you can
> do --
> if you find out, let me know, since I also have this problem with high
> rutile glazes, even with soaking and slow cooling.
>
> Chris
Longtin, Jeff on wed 31 jul 02
Hey Ian,
As long as you asked...
I fire cone 6 slip cast commercial white stoneware. Some pieces I decorate
with commercial underglazes and then cover with a clear glaze, some pieces I
clear glaze without an underglaze.
When this problem first appeared I spoke with my supplier, Mike at
Continental Clay (great resource!) and he explained the same thing, i.e.
iron-bearing bodies sometimes need a soak period in the glaze fire to allow
gases to escape.
However, if I have a white body, which in theory has no iron, what could be
causing the pinholes and what could the solution be, a soak period alone? I
tend to fire fast both in bisque and glaze so maybe I could slow both of
those down a bit but I also wonder if there could be an application solution
as well?
Do pinholes occur more as a result of application or more as a result of
firing?
Thoughts?
Thanks!
Jeff Longtin
-----Original Message-----
From: Ian Currie [mailto:ian@CURRIE.TO]
Sent: Tuesday, July 30, 2002 10:34 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: pinholes
Hi Chris
Wish I could offer some magic solution to the problem of rutile and
titanium dioxide causing pinholing. But as it is one of those perennial
problems I'm pleased to see you putting it to Clayart. If one is lucky,
a grid around the glaze you are using (grid method for those who have
not heard of it... see my website below)... a grid will *sometimes*
reveal a similar glaze with no pinholing. I have evidence on some grids
that the titanium-caused pinholes are in a zone between the more fluid
glazes where the pinholes may smooth over (not always!!) and stiff
glazes, for example the high alumina glazes, where the micro-pores in
the glaze have not started to move yet to ptoduce visible bubbles.
Apart from this I have not found any consistent thing that seems to
promote or retard this sort of pinhole. Help someone??
Just repeating something I mentioned in a previous e-mail some months
ago regarding pinholing... some iron-bearing dark clays seem to
chronically cause pinholing at midfire (^5 or 6) in oxidation. Here the
usual remedy is to change clays.
Cheers
Ian
http://ian.currie.to/
Christena Schafale wrote:
> Lisa,
>
> I suspect, though I don't know for sure, that the Spectrum "texture"
> glazes
> contain a lot of rutile to create the texture effect, and rutile is
> said to
> cause pinholing. I would guess that might be why you are having the
> problem with them and not with your other glazes. As to what you can
> do --
> if you find out, let me know, since I also have this problem with high
> rutile glazes, even with soaking and slow cooling.
>
> Chris
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Marek & Pauline Drzazga-Donaldson on wed 31 jul 02
Dear Clayarters,
I was using a once fired < 6 glaze with blue and crimson stains in on =
top of a white slip under a buff body, and found that when poured on the =
glaze did not pinhole, whereas when applied with a brush I had a great =
pinholing problem. So in my experience, and with my glaze ( a basic =
variation of a 5 x 20 ) the different application methods made a vast =
difference.
happy potting Marek http://www.moley.uk.com=20
Joanna Jorgensen on thu 1 aug 02
I work in maiolica and find that pinholes are an issue especially where
I've trimmed; recompressing the clay with a metal rib after throwing and
again after trimming helps to eliminate pinholes in my glaze which does
not flow. I imagine that this is the issue with your textured glaze, and
why it shows up more when you brush rather that dip. I do a sometimes
excruciatingly slow bisque (I have little patience and what I have I try
to save for the kids) but using a grog less clay and recompressing has
helped more than the slower bisque.
Joanna Jorgensen
Coconut Creek, FL
Christena Schafale on thu 1 aug 02
Joanna,
One tip about pinholes associated with trimming -- immediately after
trimming, I have taken to brushing a little slip from my throwing bucket
over the trimmed area and then smoothing/burnishing with a soft rubber
rib. This is very quick, leaves a clean smooth surface that blends into
the untrimmed area better, and seems to work very effectively to get rid of
that kind of pinhole, I suppose by sealing over the pores and grog
particles that are exposed when you trim.
Chris
At 09:16 AM 8/1/02 -0400, you wrote:
>I work in maiolica and find that pinholes are an issue especially where
>I've trimmed; recompressing the clay with a metal rib after throwing and
>again after trimming helps to eliminate pinholes in my glaze which does
>not flow. I imagine that this is the issue with your textured glaze, and
>why it shows up more when you brush rather that dip. I do a sometimes
>excruciatingly slow bisque (I have little patience and what I have I try
>to save for the kids) but using a grog less clay and recompressing has
>helped more than the slower bisque.
>
>Joanna Jorgensen
>
>Coconut Creek, FL
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
Consultation and Referral Specialist
Resources for Seniors
christenas@rfsnc.org
http://www.resourcesforseniors.com
Phone: (919) 713-1537
FAX: (919) 872-9574
1110 Navaho Dr, Suite 400
Raleigh, NC 27609
Lily Krakowski on sat 20 sep 03
Nancy.
"Pinholes" is like saying "tummy ache" or "skin rash." Very vague. Many
possibilities.
Essentially pinholes are the tiny passages through which water and gasses
escape in the firing. There are several factors creating gasses, but
generally it is that different materials become gas in the firing.
At first it is the organic materials. But then as different minerals begin
to melt down gasses are formed and released.
You say you fire to c.04, and I assume you fire to c.6.
If, however the clay you are using is not really meant for c.6. but is a
c.10 clay it is possible that your bisque is too low--or that it is
unsuitable for c.6.
Likeliest from your description is that the colorants you add are more
refractory than the glaze by itself. I always warn students that some
colorants are fluxes and some are refractory. A green glaze made with
copper will melt earlier than the glaze plain, and the same glaze made green
by chrome will melt later than the glaze plain.
Having said that as the glazes come from RonJohn's book I expect you are
firing too fast. And if you do not have one of those digital gadzookies you
will have to take care of it yourself. Start by turning the switches to
medium for 1/4 hour after the cones have gone down. SOME ONE--MAYBE RON/JOHN
CAN TELL YOU BETTER. (Or Redoubtable Snail will)
This process should allow the glaze to heal (flow over) the pinholes.
There are other causes of pinholing--glaze application for one--too thick,
too thin--but I suspect it is the refractoriness of your added materials.
And I suggest Ceramic Faults and their Remedies by Harry Fraser, A & C
Black, London as a most excellent book for you to get.
You write "colour" and your e mail address has mission in it....So I assume
you are in some Brit location? A missionary? Way off where? Hence I do
not suggest you try The Potters' Shop, since it is in Massachusets.
Good luck
Lili Krakowski
Constableville, N.Y.
Be of good courage....
The Hallquist's on sun 21 sep 03
Lily,
I see what you mean about the tummy ache stuff. I was not very specific. I
do have a computerized kiln. And I fire it pretty similar to John and Ron's
firing schedule in there book. I soak the kiln at top temp for 20 mins. I
use bmix clay cone 5. Now, I think what you are saying about the oxides may
be the case. Another post indicated a finer sieve may be the answer, so I
will try this first and then go from there. Don't want to change more than
one thing at a time. By the way, I live in Mission, Canada. It's a very
small town, best kept secret if you ask me. We do have a Monestary here
though. Thanks for the recommendation on the book. I will try to locate
it.
Thanks so much for your help.
Nancy
----- Original Message -----
From: "Lily Krakowski"
To:
Sent: Saturday, September 20, 2003 4:17 PM
Subject: Pinholes
> Nancy.
>
> "Pinholes" is like saying "tummy ache" or "skin rash." Very vague. Many
> possibilities.
>
> Essentially pinholes are the tiny passages through which water and gasses
> escape in the firing. There are several factors creating gasses, but
> generally it is that different materials become gas in the firing.
>
> At first it is the organic materials. But then as different minerals
begin
> to melt down gasses are formed and released.
>
> You say you fire to c.04, and I assume you fire to c.6.
>
> If, however the clay you are using is not really meant for c.6. but is a
> c.10 clay it is possible that your bisque is too low--or that it is
> unsuitable for c.6.
>
> Likeliest from your description is that the colorants you add are more
> refractory than the glaze by itself. I always warn students that some
> colorants are fluxes and some are refractory. A green glaze made with
> copper will melt earlier than the glaze plain, and the same glaze made
green
> by chrome will melt later than the glaze plain.
>
> Having said that as the glazes come from RonJohn's book I expect you are
> firing too fast. And if you do not have one of those digital gadzookies
you
> will have to take care of it yourself. Start by turning the switches to
> medium for 1/4 hour after the cones have gone down. SOME ONE--MAYBE
RON/JOHN
> CAN TELL YOU BETTER. (Or Redoubtable Snail will)
>
> This process should allow the glaze to heal (flow over) the pinholes.
>
> There are other causes of pinholing--glaze application for one--too thick,
> too thin--but I suspect it is the refractoriness of your added materials.
>
> And I suggest Ceramic Faults and their Remedies by Harry Fraser, A & C
> Black, London as a most excellent book for you to get.
>
> You write "colour" and your e mail address has mission in it....So I
assume
> you are in some Brit location? A missionary? Way off where? Hence I do
> not suggest you try The Potters' Shop, since it is in Massachusets.
>
> Good luck
>
>
>
>
> Lili Krakowski
> Constableville, N.Y.
>
> Be of good courage....
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Tony Hansen on sun 21 sep 03
Check this page also:
http://www.digitalfire.ab.ca/cermat/education/129.php
There is tons of possibilities outlined on it.
-------8<--------
Nancy.
\"Pinholes\" is like saying \"tummy ache\" or \"skin rash.\" Very vague. Many
possibilities.
Essentially pinholes are the tiny passages through which water and gasses
escape in the firing. There are several factors creating gasses, but
generally it is that different materials become gas in the firing.
At first it is the organic materials. But then as different minerals begin
to melt down gasses are formed and released.
You say you fire to c.04, and I assume you fire to c.6.
If, however the clay you are using is not really meant for c.6. but is a
c.10 clay it is possible that your bisque is too low--or that it is
unsuitable for c.6.
Likeliest from your description is that the colorants you add are more
refractory than the glaze by itself. I always warn students that some
colorants are fluxes and some are refractory. A green glaze made with
copper will melt earlier than the glaze plain, and the same glaze made green
by chrome will melt later than the glaze plain.
Having said that as the glazes come from RonJohn\'s book I expect you are
firing too fast. And if you do not have one of those digital gadzookies you
will have to take care of it yourself. Start by turning the switches to
medium for 1/4 hour after the cones have gone down. SOME ONE--MAYBE RON/JOHN
CAN TELL YOU BETTER. (Or Redoubtable Snail will)
This process should allow the glaze to heal (flow over) the pinholes.
There are other causes of pinholing--glaze application for one--too thick,
too thin--but I suspect it is the refractoriness of your added materials.
And I suggest Ceramic Faults and their Remedies by Harry Fraser, A & C
Black, London as a most excellent book for you to get.
You write \"colour\" and your e mail address has mission in it....So I assume
you are in some Brit location? A missionary? Way off where? Hence I do
not suggest you try The Potters\' Shop, since it is in Massachusets.
Good luck
Lili Krakowski
Constableville, N.Y.
Be of good courage....
______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
--------
Tony Hansen, Digitalfire Corp.
P. Canupp on tue 24 feb 04
I decided to write a new message instead of reading the several hundred
messages posted about pinholes. In my last two firings I have had pinholes.
I am using the same batch of glaze which I have successfully fired several
times prior with no pinholes. I am using the same clay also. In my last
firing I also soaked the pieces several hours longer than usual. In all
cases I fired to cone 6 in oxidation.
Also, on a different glaze (with the same base ingredients) I had ugly
bloating things (which were actually open with the clay exposed in the
middle of the bloat).
Any help on these strange phenomena?
Elizabeth
S.E.W. on tue 24 feb 04
It sounds like you either used to much glaze or your bisque was not =
mature. Did you soak the pieces on the glaze fire or the greenware fire? =
If you over apply a glaze and the piece isn't mature, it will cause the =
blistering that you described. I hope that helps!
Rachel
Pamela Watkins on thu 26 feb 04
Hi Elizabeth,
I'll take a stab at the pinhole problem eventhough there are more highly qualified experts, otherwise known as glaze gurus on the list. My bet would be too thick of an application of the glaze. Water may have evaporated from a loose lid or container sitting around open or if the glaze hasn't been used a while-add a bit more water and thin it out. Or too thick from the method of application, ie dipped 3 times instead of two...what have you. I wouldn't think a longer soak would be the culprit, but then again the gurus could mark me wrong. May be worth a look at the archives. The craters could be from the glaze not reaching the melt stage or from impurtities. I'd try firing thoes pieces again, a cone higher. Just my 2'sense' worth. Good Luck!
Peace,
Pamela
~jaq
"P. Canupp" wrote:
I decided to write a new message instead of reading the several hundred
messages posted about pinholes. In my last two firings I have had pinholes.
I am using the same batch of glaze which I have successfully fired several
times prior with no pinholes. I am using the same clay also. In my last
firing I also soaked the pieces several hours longer than usual. In all
cases I fired to cone 6 in oxidation.
Also, on a different glaze (with the same base ingredients) I had ugly
bloating things (which were actually open with the clay exposed in the
middle of the bloat).
Any help on these strange phenomena?
Elizabeth
______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org
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Ron Roy on thu 26 feb 04
Hi Elizabeth,
Sounds like your bisque firing was either too fast - not enough oxygen or
not high enough. This would leave unburned oraganics in the clay that will
overfire your clay and produce the gas and bubbles and bloating.
If - when you refire any of those pieces - the problem gets worse - then
you know that is the problem. It's the same as overfired clay - was it a
new batch of clay or have you changed the way you bisque - or maybe the
ware is thicker than usual?
RR
>I decided to write a new message instead of reading the several hundred
>messages posted about pinholes. In my last two firings I have had pinholes.
> I am using the same batch of glaze which I have successfully fired several
>times prior with no pinholes. I am using the same clay also. In my last
>firing I also soaked the pieces several hours longer than usual. In all
>cases I fired to cone 6 in oxidation.
>
>Also, on a different glaze (with the same base ingredients) I had ugly
>bloating things (which were actually open with the clay exposed in the
>middle of the bloat).
>
>Any help on these strange phenomena?
>
>Elizabeth
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Judi Buchanan on thu 26 feb 04
.If I am reading your description of the "things" correctly, the
possible answer is bisque dust. I have had the glaze look like it had
curled back and exposed the clay when I had left the sanding dust on the
bisque. (Two no nos sanding and not wiping the bisque.)
Also, on a different glaze (with the same base ingredients) I had ugly
bloating things (which were actually open with the clay exposed in the
middle of the bloat).
Any help on these strange phenomena?
Elizabeth
WHC228@AOL.COM on thu 26 feb 04
Elizabeth
Sanding can be a problem. If the paper has silicon carbide in it and any of
the silicon carbide is left behind, there will be pinholing and or nasty
blisters.
Try putting some of the abrasive on a shard a glaze it. See what you get.
I once used some abrasive cloth that looked a lot like window screen, and it
left little flecks on my pots. I couldn't even see them. Once they were
discovered and I changed how I finished my ware, the blisters disappeared.
Bill
Carole Fox on fri 27 feb 04
Speaking of pinholes...let's say you put too much glaze on a piece and it
pinholes. Is the piece still functional? Can it be sold as a second or is it
just trash?
Carole Fox
Silver Fox Pottery
Elkton, MD
thesilverfox@dol.net
Pamela Watkins on fri 27 feb 04
Carole Fox wrote:
Speaking of pinholes...let's say you put too much glaze on a piece and it
pinholes. Is the piece still functional? Can it be sold as a second or is it
just trash?
Hi Carol,
Any ole Jack (jaq) or Joe may look at your piece with pinholes and remark, "interesting". On the other hand, anyone that knows anything about pottery, and not to mention glazing would look at the piece and remark, "ooh, glaze error, too bad you gotta smash it, that piece had nice form...." or something to that extent. I suppose the choice is yours, but I personally wouldn't advocate selling any "seconds" ever......the glaze and the whole shebang has to work and if not, very few eyes will gaze on that pot before it is smashed. BTW my smashed shards are reborn into a mosaic, for the sake of sentimentalitly. Christy in Connecticut is tile-ing the exterior back foundation wall of here home with smashed no-goods and I was happy to smash two mugs just for her as a momento. That grolleg-colored clay with laminated pattern suffered a tiny s crack. The other two, sold. Hope to have been of some help.
Peace,
Pamela
~jaq
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Lili Krakowski on mon 13 nov 06
Nancy tells us her Floating Blue is fired in the cooler section of her
c.6 ox. kiln.
All was "...beautiful with the exception of my floating blue and a mug on
the shelf with the floating blue pieces." She uses Chappells recipe with
GB.
The pinholes in the FB pieces were invisible till rubbed...when they
popped..and double dipped rims did ok. "So now I have a 5 gallon bucket
of glaze that I can't use unless I can find a fix for the problem..."
First I would let the 5 gallons dry out COMPLETELY. This generally means
pouring some of the slop into a wide flat pan, such as kitty litter pan,
letting dry totally, bagging, repeating this till all is dry. I never
have
managed to get 5 gallons of glaze to dry TOTALLY in the bucket..
Well, maybe after years. Then you have a mix that you can start testing
with.
I may be the only potter with only one FB glaze recipe. (Never use it)
The glaze recipe I have is high soda, high boron with Fe2O3 2%
Cobalt OXIDE 1 % , Dark Rutile 4%. I assume the other recipes are
pretty similar.
So. Back to pinholes. Pinholes are attributed to gases escaping from
organic matter in the clay body, or from the decomposition of
certain materials in body or glaze. When you have heated
mashed potatoes on the stove you know that --in the case of potatoes--steam
rises, lifts a spot on the surface and goes "plop". (Much like primeval
slime
in horror sci-fi flicks) When you are heating peas, however, there are
no"plops", because the steam has no difficulty getting out. (Some clay
bodies have more gas forming materials in them than others; or why one
should
test glazes on several bodies, and/or over white slip as well as body
proper.)
Ok. So if the glaze is not runny enough, not melted enough when specific
gases need to escape, there will be a "plop" and if that "plop" is
not able to smooth out fully, there will be a little hole left. (Some
materials
will gasify [is there such a word?] only at temps awful close
to one's firing temp--i.e. at end of firing.)
IF this little hole holds some melted glaze, then there will be a tiny
"blister"
and the tiny blister will pop when you rub the surface.
Hobart Cowles considered a GOOD magnifying glass, such as a jeweler's
loupe, an ESSENTIAL glazing tool. I have always found it so.
When you get your magnifying glass you will see the situation
much more clearly.
The first suggestion always is a higher bisque. Why? because more
stuff that needs to burn out from the clay will have burned out
before you glaze. But if you already bisque high enough
then a bit more flux in the glaze may help.
You say you used Chappell's recipe, and Gerstley Borate. Two points:
I checked Abebooks and they have 1977 first editions and 1991 revised
editions. Pub dates are about 2 years after finished manuscripts.
Meaning that the GB Chappell used probably was very very
different from what you are using. (Or why I consider GB totally
untrustworthy, and recalculate all I can to frits.)
Second suggestion : add a bit more flux, so that your glaze
melts a tidge earlier. Or you can leave your kiln longer on medium
or soak a bit longer on high. (I DO NOT have a kiln with ramps,
someone who does will have to tell you how that is done
with a digital kiln.)
If the glaze melts a tidge earlier, OR is given a bit more time
before the surface hardens, there is a chance the glaze
will "heal" better. Why by the way is it in the coolest part
of the kiln? Can you try it in warmer climes?
I guess the double dip gave better results because the
top glaze actually fluxed the FB a bit....or perhaps the thicker layer--
delayed the surface cooling. Fraser tells us too thin application
of the glaze also may be a cause of pinholing,
as there is not enough glaze to fill all the tiny holes in the clay body
surface.
I want to add that Harry Fraser's "Ceramic Faults and their Remedies"
is a wonderful book that I cannot recommend too much.
I hope some of this helps. Pinholing is one of those really pesky
glaze problems. And, just to be miserable, there are glazes
that exploit the "plop effect" for decorative purposes.
Lili Krakowski
Be of good courage
Nancy on mon 13 nov 06
Lili
Thank you for all the wonderful info. Yes I have GB and only use it in
this one recipe. I have tried bisque firing to cone 04 and I lengthened
my glaze firing schedule all trying to get rid of this FB pinholing. I
have not tried double dipping the FB to see if that helps because FB is
a pretty runny glaze...it's beautiful when it does work right. I keep
it in the cooler part of the kiln as it was suggested that when FB is
fired to cone 6 and up it can be very ugly. My cooler part is about
cone 5 1/2 (as best I can figure). Now I guess I have to dump the glaze
and try the new one Ron posted and eliminate the GB and hope this helps
my problem. I am in the process of drying out my washed ash and as I
don'thave a huge studio with a lot of extra space, I will try to dry out
the FB and see what I can do with it down the road.
Thanks again!
Nancy
www.hilltoppottery.com
Lili Krakowski wrote:
> Nancy tells us her Floating Blue is fired in the cooler section of her
> c.6 ox. kiln.
>
> All was "...beautiful with the exception of my floating blue and a mug on
> the shelf with the floating blue pieces." She uses Chappells recipe with
> GB.
> The pinholes in the FB pieces were invisible till rubbed...when they
> popped..and double dipped rims did ok. "So now I have a 5 gallon bucket
> of glaze that I can't use unless I can find a fix for the problem..."
>
> First I would let the 5 gallons dry out COMPLETELY. This generally means
> pouring some of the slop into a wide flat pan, such as kitty litter pan,
> letting dry totally, bagging, repeating this till all is dry. I never
> have
> managed to get 5 gallons of glaze to dry TOTALLY in the bucket..
> Well, maybe after years. Then you have a mix that you can start testing
> with.
>
> I may be the only potter with only one FB glaze recipe. (Never use it)
> The glaze recipe I have is high soda, high boron with Fe2O3 2%
> Cobalt OXIDE 1 % , Dark Rutile 4%. I assume the other recipes are
> pretty similar.
>
> So. Back to pinholes. Pinholes are attributed to gases escaping from
> organic matter in the clay body, or from the decomposition of
> certain materials in body or glaze. When you have heated
> mashed potatoes on the stove you know that --in the case of
> potatoes--steam
> rises, lifts a spot on the surface and goes "plop". (Much like primeval
> slime
> in horror sci-fi flicks) When you are heating peas, however, there are
> no"plops", because the steam has no difficulty getting out. (Some clay
> bodies have more gas forming materials in them than others; or why one
> should
> test glazes on several bodies, and/or over white slip as well as body
> proper.)
>
> Ok. So if the glaze is not runny enough, not melted enough when specific
> gases need to escape, there will be a "plop" and if that "plop" is
> not able to smooth out fully, there will be a little hole left. (Some
> materials
> will gasify [is there such a word?] only at temps awful close
> to one's firing temp--i.e. at end of firing.)
> IF this little hole holds some melted glaze, then there will be a tiny
> "blister"
> and the tiny blister will pop when you rub the surface.
>
> Hobart Cowles considered a GOOD magnifying glass, such as a jeweler's
> loupe, an ESSENTIAL glazing tool. I have always found it so.
> When you get your magnifying glass you will see the situation
> much more clearly.
>
> The first suggestion always is a higher bisque. Why? because more
> stuff that needs to burn out from the clay will have burned out
> before you glaze. But if you already bisque high enough
> then a bit more flux in the glaze may help.
>
> You say you used Chappell's recipe, and Gerstley Borate. Two points:
> I checked Abebooks and they have 1977 first editions and 1991 revised
> editions. Pub dates are about 2 years after finished manuscripts.
> Meaning that the GB Chappell used probably was very very
> different from what you are using. (Or why I consider GB totally
> untrustworthy, and recalculate all I can to frits.)
>
> Second suggestion : add a bit more flux, so that your glaze
> melts a tidge earlier. Or you can leave your kiln longer on medium
> or soak a bit longer on high. (I DO NOT have a kiln with ramps,
> someone who does will have to tell you how that is done
> with a digital kiln.)
>
> If the glaze melts a tidge earlier, OR is given a bit more time
> before the surface hardens, there is a chance the glaze
> will "heal" better. Why by the way is it in the coolest part
> of the kiln? Can you try it in warmer climes?
>
> I guess the double dip gave better results because the
> top glaze actually fluxed the FB a bit....or perhaps the thicker layer--
> delayed the surface cooling. Fraser tells us too thin application
> of the glaze also may be a cause of pinholing,
> as there is not enough glaze to fill all the tiny holes in the clay body
> surface.
>
> I want to add that Harry Fraser's "Ceramic Faults and their Remedies"
> is a wonderful book that I cannot recommend too much.
>
> I hope some of this helps. Pinholing is one of those really pesky
> glaze problems. And, just to be miserable, there are glazes
> that exploit the "plop effect" for decorative purposes.
>
>
>
> Lili Krakowski
> Be of good courage
>
> ______________________________________________________________________________
>
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Lili Krakowski on tue 14 nov 06
After my post about pinholing, several were posted, to list or to me, about
OVERFIRING as a cause of p.h.
How can that be?
Well, if one thinks of glaze firing as a line dance, with a lot of "change
your partners" and "Left foot in", and stuff like that,
one gets a picture of what goes on.
Materials interact, but they interact only under certain circumstances. We
all KNOW--or should-- that steam is formed early on in the firing and "steps
out". Next come "carbonaceous materials" which burn out in their turn,
though not all at once.
And on and on.
As temperatures rise, different materials melt, start to disassociate,
decompose, and release gases. Wasn't it just a few days
ago that there was a post about MnO2 and at what temp it starts to "fall
apart"?
In my opinion, all obtained pragmatically, (read "firing disasters") the
ideal firing temp for a glaze is when ALL the gases from CERTAIN materials
have stepped out, and the gases from OTHER materials have not yet manifested
themselves.
And there are materials--Fluorspar, Cryolite, and, tangentially Bone
Ash--that cause extra gas production causing ructions which can create
lovely effects. Wood Ash can do the same.
One also must consider that these changes occur in the clay body as
well...so that a glaze will be affected by gases from the body...
(And it is exactly because certain materials enter the dance "late", while
others enter early and leave early that some materials are better in low
temp glazes and others in high. (Nickel is a good example).
Anyway. That is what I think....
Nancy on tue 14 nov 06
Lili
I may have been one of those previously. Ron explained to me a while
back that the chemicals may not have burned out completely the the kiln
cooled too fast which caused the pinholes....of course I'm sure he used
all the appropriate terminology but in layman's terms, that is how I
took his explanation. I have, in the past, used FB with much success
but with this GB I have now, it may be the problem so my solution is to
try Ron's revision and see if it helps. I'm not firing everything in FB
but I do find people tend to gravitate toward's blue. This is my last
attempt at FB and then I'm gonna find something different. I do love a
glaze from Amaco Potters Choice called Blue Rutile that is a gorgeous
blue. I buy it dry for about $60 for 25lbs. So I think I may become an
ex FB glazer if this next idea doesn't work. Sometimes it's easier to
just move on
Nancy
www.hilltoppottery.com
Lili Krakowski wrote:
> After my post about pinholing, several were posted, to list or to me,
> about
> OVERFIRING as a cause of p.h.
>
> How can that be?
>
> Well, if one thinks of glaze firing as a line dance, with a lot of
> "change
> your partners" and "Left foot in", and stuff like that,
> one gets a picture of what goes on.
>
> Materials interact, but they interact only under certain
> circumstances. We
> all KNOW--or should-- that steam is formed early on in the firing and
> "steps
> out". Next come "carbonaceous materials" which burn out in their turn,
> though not all at once.
> And on and on.
>
> As temperatures rise, different materials melt, start to disassociate,
> decompose, and release gases. Wasn't it just a few days
> ago that there was a post about MnO2 and at what temp it starts to "fall
> apart"?
>
> In my opinion, all obtained pragmatically, (read "firing disasters") the
> ideal firing temp for a glaze is when ALL the gases from CERTAIN
> materials
> have stepped out, and the gases from OTHER materials have not yet
> manifested
> themselves.
>
> And there are materials--Fluorspar, Cryolite, and, tangentially Bone
> Ash--that cause extra gas production causing ructions which can create
> lovely effects. Wood Ash can do the same.
>
> One also must consider that these changes occur in the clay body as
> well...so that a glaze will be affected by gases from the body...
>
> (And it is exactly because certain materials enter the dance "late",
> while
> others enter early and leave early that some materials are better in low
> temp glazes and others in high. (Nickel is a good example).
>
> Anyway. That is what I think....
>
> ______________________________________________________________________________
>
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
nori on sun 25 may 08
This is a multi-part message in MIME format.
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hi, everyone.
i got lots of great suggestions about my pinholes / craters. and as
usual, i learned a lot... and not just about my immediate problem.
that's the beauty of clayart, for me.
thought i'd give you a follow up.... a terrific potter who's in the
same building as me stopped by. i took advantage of his visit & asked
him to look at the glaze defects. he knows me, knows the studio, etc...
and his very well-informed guess was DUST.
i've been crazy busy, and probably didn't do as good a job as i usually
do of wiping down my bisque.
and looking more closely at the pots, i also noticed a few places where
the glaze skipped.... bare clay showing through. i have some VAGUE
memory of using lotion on my hands, thinking how dumb that was just
before glazing, washing my hands & going ahead. bet there was some
residue that acted as a resist.
owell, i guess i need to learn the lesson yet again... slow down, think,
then act.
thanks again.
sabra
--
Clifton, Norwich & Sabra
My pottery cat clay
Our studio crocus clay works
My charity A little effort + no money = a big difference!
sample soap
--------------090208070801060601030708
Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: 7bit
hi, everyone.
i got lots of great suggestions about my pinholes / craters. and as
usual, i learned a lot... and not just about my immediate problem.
that's the beauty of clayart, for me.
thought i'd give you a follow up.... a terrific potter who's in the
same building as me stopped by. i took advantage of his visit &
asked him to look at the glaze defects. he knows me, knows the studio,
etc... and his very well-informed guess was DUST.
i've been crazy busy, and probably didn't do as good a job as i usually
do of wiping down my bisque.
and looking more closely at the pots, i also noticed a few places where
the glaze skipped.... bare clay showing through. i have some VAGUE
memory of using lotion on my hands, thinking how dumb that was just
before glazing, washing my hands & going ahead. bet there was some
residue that acted as a resist.
owell, i guess i need to learn the lesson yet again... slow down,
think, then act.
thanks again.
sabra
--------------090208070801060601030708--
Eleanor on thu 18 nov 10
Following the good advice from Clayart gurus about heat work, I fired
a glaze batch using a new firing schedule. The results were beautiful!
There were two casseroles glazed with a combination of M^6G glazes and
some tried-and-true others; the effects were lovely. Then I looked
inside--- senior moment---I had forgotten to glaze the insides.
So I applied my usual liner glaze and refired with the next glaze
firing. The casseroles were placed at about the middle of the kiln.
All the newly-glazed pots came out perfect but the casseroles were
literally covered with pinholes. They are now hammer-ready.
What happened and why?
Would refiring at bisque temperature (^04) smooth out the pinholes?
Eleanor Kohler
Centerport, NY
Happy Thanksgiving to all!
".... philosophers lay down many precepts fair in argument but not
applicable in use"
--Sir Francis Bacon
Lee Love on thu 18 nov 10
On Thu, Nov 18, 2010 at 7:58 AM, Eleanor wrote:
> Would refiring at bisque temperature (^04) smooth out the pinholes?
I have scraped thick glaze off the wall of the glaze bucket and rubbed
it into the pinholes and refire to good effect.
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Ron Roy on thu 18 nov 10
Hi Eleanor,
Firing to the same cone twice results in at least an extra cone higher
than the first time.
Either your glazes or your clay are not designed for cone 7 - or both.
I don't think going to 04 will help much but going to cone 6 again
will probably make it worse.
RR
Quoting Eleanor :
> Following the good advice from Clayart gurus about heat work, I fired
> a glaze batch using a new firing schedule. The results were beautiful!
>
> There were two casseroles glazed with a combination of M^6G glazes and
> some tried-and-true others; the effects were lovely. Then I looked
> inside--- senior moment---I had forgotten to glaze the insides.
>
> So I applied my usual liner glaze and refired with the next glaze
> firing. The casseroles were placed at about the middle of the kiln.
>
> All the newly-glazed pots came out perfect but the casseroles were
> literally covered with pinholes. They are now hammer-ready.
>
> What happened and why?
>
> Would refiring at bisque temperature (^04) smooth out the pinholes?
>
> Eleanor Kohler
> Centerport, NY
>
> Happy Thanksgiving to all!
>
>
>
>
>
>
>
>
> ".... philosophers lay down many precepts fair in argument but not
> applicable in use"
>
> --Sir Francis Bacon
>
paul gerhold on fri 19 nov 10
Eleanor,
My experience would say that once you get pinholes in a glaze refiring will
do nothing but make them worse unless you refire high enough so the glaze
almost runs or actually does run. If the casseroles have a lot of value t=
o
you, consider putting on a base and then firing till the glaze runs and
then grinding the bottom. Process similar to crystal firing. Sometimes,
unexpectedly beautiful results will be achieved.
Paul
Brad Sondahl on fri 25 may 12
I have one glaze that is prone to pinholing--it is a green with Copper
Carbonate, and I've tried many variations with no perfect results. The
interesting thing is where the pinholes happen--anywhere that the surface
of the clay had been disturbed in footing--particularly on the rims, where
they get scraped while being centered, or in the case of berry bowls, in
the area around the holes punched in the base where I've cleaned them up
with a tool to smooth them. Thus my hypothesis would be that small holes
in the surface of the clay act in a miniscule way like slightly larger
holes do--they resist filling with glaze, and create mini craters in the
glaze. The other likely place where this would happen would be on the
bottoms where trimming has occurred, but I paint slip on those areas after
footing to avoid pinholing in that area. It is likely there are strictly
glaze related sources of pinholing as well, but I'm quite sure the surface
of the clay plays a role in some pinholing.
One solution that has worked to avoid the problem has been to paint another
nonpinholing glaze on in a thin coat in the areas prone to pinholing before
dipping it in the susceptible glaze.
Brad Sondahl sondahl.com
Snail Scott on fri 25 may 12
On May 25, 2012, at 10:50 AM, Brad Sondahl wrote:
> I have one glaze that is prone to pinholing...The
> interesting thing is where the pinholes happen--anywhere that the surface
> of the clay had been disturbed in footing--particularly on the rims, wher=
e
> they get scraped while being centered, or in the case of berry bowls, in
> the area around the holes punched in the base where I've cleaned them up
> with a tool to smooth them...
This is especially noticeable with work that has been
thrown and trimmed, and the sand or grog in the clay
body has been snagged by the tool and caused a
small gap as it is pulled. Re-smoothing the clay
surface is easy enough in some areas, but tricky in
others, such as the drainage holes you mentioned.
I find that dampening the bisque before glazing helps
the first layer of glaze to penetrate the small pits caused
by carving and trimming. Once this layer has been
established, even if it is very thin, the subsequent layer(s)
of glaze will flow and fill during firing, and seldom develop
pinholes in the vulnerable areas.
-Snail
Gayle Bair on fri 25 may 12
Hi Brad,
I also use a very thinned down glaze application on pieces which I know
from experience will pinhole except I dip the entire piece instead of
brushing it on. It totally eliminates pinhole for me.
I'd suggest using the thinned down glaze and just dip your bowls into it. I
find brushing takes way too long especially with berry bowls. By the time I
get all the pieces dipped they are ready for the next glaze dipping which
I prefer to be slightly thinned down. If it's too thick the glaze fills up
the holes. If that occurs I blow into the bowl right after dipping to make
sure the holes haven't filled up with glaze.
So what do you use to make the holes? I got tired of doing them by hand and
am using a small rechargeable drill..... it's much cleaner and faster.
Best regards,
Gayle
Gayle Bair Pottery
gayle@claybair.com
www.claybair.com
On Fri, May 25, 2012 at 8:50 AM, Brad Sondahl wrote:
> Snip>
> One solution that has worked to avoid the problem has been to paint anoth=
er
> nonpinholing glaze on in a thin coat in the areas prone to pinholing befo=
re
> dipping it in the susceptible glaze.
>
ivor and olive lewis on sun 27 may 12
Dear Brad Sondahl,
It would seem to me that the glaze development has been arrested before al=
l
possible physical and chemical reactions are completed.
I would suggest three possible ways of correcting these embarrassing
defects. The first is to extend your firing, heating until the next higher
cone falls. The second would be to holding at a constant temperature.for a
period of time after your marker cone has fallen. The third is to reduce th=
e
rate of heating as you approach the setting of your usual cone, allowing th=
e
glaze more time to develop and impose its molten physical properties on the
clay body.
Regarding the idea of burnishing to seal minute scars caused by turning. It
is possible that the way your glaze is formulated is preventing the fusing
fluid from flowing into the cavities cause by dislodged grains of grog
because it is highly viscous, has a low surface tension and inadequate
capillary surface energy.
Regards,
Ivor Lewis,
REDHILL,
South Australia
ronroy@CA.INTER.NET on sun 27 may 12
Hi Brad,
I think you may just have a stiff glaze there - some of the oxides we
use have a high viscosity and/or a high surface tension - these can be
replaced with others that contribute lower viscosity and/or lower
surface tension.
This can overcome the problem you have because the glaze will flow
better at top temperature and will heal the pin holes - which normally
happens with most glazed over trimmed areas.
The are two tables in the Hamer book listing oxides in order of
viscosity and surface tension - high to low.
The oxide with the highest viscosity and the highest surface tension
is Al2O3 - that explains why - when you have a runny glaze one of the
fixes is to add clay.
The oxide with the lowest viscosity and lowest surface tension is K2O
along with Na2O and Li2O - so adding them to a glaze will help flow
and would help heal any pin holing problem.
RR
The next highest oxide may be the right one for this situation - B2O3.
Anyway - if you want to send me the recipe I can make some suggestions
- certainly worth a try instead of all that extra work others are
suggesting.
Quoting Brad Sondahl :
> I have one glaze that is prone to pinholing--it is a green with Copper
> Carbonate, and I've tried many variations with no perfect results. The
> interesting thing is where the pinholes happen--anywhere that the surface
> of the clay had been disturbed in footing--particularly on the rims, wher=
e
> they get scraped while being centered, or in the case of berry bowls, in
> the area around the holes punched in the base where I've cleaned them up
> with a tool to smooth them. Thus my hypothesis would be that small holes
> in the surface of the clay act in a miniscule way like slightly larger
> holes do--they resist filling with glaze, and create mini craters in the
> glaze. The other likely place where this would happen would be on the
> bottoms where trimming has occurred, but I paint slip on those areas afte=
r
> footing to avoid pinholing in that area. It is likely there are strictly
> glaze related sources of pinholing as well, but I'm quite sure the surfac=
e
> of the clay plays a role in some pinholing.
> One solution that has worked to avoid the problem has been to paint anoth=
er
> nonpinholing glaze on in a thin coat in the areas prone to pinholing befo=
re
> dipping it in the susceptible glaze.
> Brad Sondahl sondahl.com
>
David Woof on mon 28 may 12
Hi Brad=3D2C Everyone=3D2C
=3D20
Brad you are getting close to something significant when you opine that the=
=3D
clay surface has something to do with the forming of pin holes.=3D20
=3D20
However one is complicating a simple process with all that fussing with pai=
=3D
nting over your glaze or trimmed clay body with other glazes=3D2C slips etc=
. =3D
This may lead one to special glaze effects=3D2C but doesn't get one any clo=
se=3D
r to the foundation solutions to the glaze pin hole problem.
=3D20
Proper trimming followed by wooden tool burnishing=3D2C while wheel is stil=
l =3D
turning=3D2C of all trimmed or post disturbing of thrown surfaces is a simp=
le=3D
technique to close those offending little craters that contribute to air p=
=3D
ockets beneath the applied glaze. Bisqueing at ^ 010 and deflocculating uo=
=3D
ur glaze with "Glass Magic" in addition to suspending it with bentonite=3D2=
C =3D
two to five percent (2-5%)=3D2C along with CMC Gum will allow the glaze to =
fl=3D
ow and spread wonderfully on all sorts of complex planes and surfaces.=3D20
=3D20
(Plus you get a durable=3D2C no powdering dried glaze surface for handling =
wh=3D
ile applying over the glaze brush work and loading the ware.)
=3D20
There are glaze formulas that actually do require flocculation and which ma=
=3D
y work better on pots fired at higher bisque temps=3D2C but in most cases d=
ef=3D
locculating is a better way to go in spite of what has been historically pu=
=3D
blished and repeated by generations of "experts" adnauseum. So try it if yo=
=3D
u have the curiosity and cahooneys for an adventure where you might possibl=
=3D
y learn something new and find a simple and effective solution.=3D20
=3D20
Trapped air may be part of the problem=3D2C as well as off gassing during i=
ni=3D
tial glaze fluxing and melt but there is more:
=3D20
****Ron R speaks below of glaze materials used to adjust glaze viscosity du=
=3D
ring firing etc.=3D20
=3D20
This combined with firing protocols that give glazes time to heal the off g=
=3D
assing craters that sometimes develop during firing on certain glazes will =
=3D
be very beneficial.
=3D20
I would encourage that you read again and make a further study of what he i=
=3D
s talking about.
=3D20
It seems so human nature to want the quick "how to now answer" and to negle=
=3D
ct time=3D2C study and thought to make the information our own. The initia=
l =3D
factual answer is the foundation to build on and the resource for thinking =
=3D
and future problem solving. Check it out...prove it to your self=3D2C=3D2C=
=3D2C=3D
=3D2C make it your own.
=3D20
Tony C says he would smack students for sponging their pots!
=3D20
I agree=3D2C except for special effects=3D2C(Yes Lee=3D2C yes I know!) why=
would=3D
anyone wish to compromise the absorbency we depend on to cause the glaze m=
=3D
aterials to adhere to the pot's surface? Just another fussy step to slow d=
=3D
own production when a properly deflocculated glaze will flow and fill.
=3D20
One last thought=3D3B if the glaze you are applying appears as filled with =
ma=3D
ny tiny bubbles on its surface as it first sets on the pot=3D2C thin the gl=
az=3D
e a bit using the CMC/water glaze mixing solution.
=3D20
If you dip a bone dry finger in your glaze and bubbles rise and break at th=
=3D
e surface=3D2C this is from air trapped in the fingerprints and micro folds=
a=3D
nd contours of your skin=3D3B your glaze is just right to flow and do the s=
am=3D
e on your pot.
=3D20
If the glaze on your dipped finger forms a thicker smooth coating=3D2C the =
gl=3D
aze is most likely trapping air on the surface of your skin and will do the=
=3D
same on your pot!!! Thin it (just a bit) and test as described until it ce=
=3D
ases to do what you don't want it to do!!!=3D20
=3D20
David Woof =3D20
=3D20
___________________________________________________________________________=
=3D
_
=3D20
a. Re: pinholes=3D20
Posted by: "ronroy@CA.INTER.NET" ronroy@CA.INTER.NET=3D20
Date: Sun May 27=3D2C 2012 4:07 pm ((PDT))=3D20
=3D20
Hi Brad=3D2C=3D20
=3D20
I think you may just have a stiff glaze there - some of the oxides we use h=
=3D
ave a high viscosity and/or a high surface tension - these can be replaced =
=3D
with others that contribute lower viscosity and/or lower surface tension. T=
=3D
his can overcome the problem you have because the glaze will flow better at=
=3D
top temperature and will heal the pin holes - which normally happens with =
=3D
most glazed over trimmed areas. The are two tables in the Hamer book listin=
=3D
g oxides in order of viscosity and surface tension - high to low. The oxide=
=3D
with the highest viscosity and the highest surface tension is Al2O3 - that=
=3D
explains why - when you have a runny glaze one of the fixes is to add clay=
=3D
. The oxide with the lowest viscosity and lowest surface tension is K2O alo=
=3D
ng with Na2O and Li2O - so adding them to a glaze will help flow and would =
=3D
help heal any pin holing problem. RR The next highest oxide may be the righ=
=3D
t one for this situation - B2O3. Anyway - if you want to send me the recipe=
=3D
I can make some suggestions- certainly worth a try instead of all that ext=
=3D
ra work others are suggesting. =3D20
=3D20
Quoting Brad Sondahl :=3D20
=3D20
I have one glaze that is prone to pin holing--it is a green with Copper> Ca=
=3D
rbonate=3D2C and I've tried many variations with no perfect results. The in=
te=3D
resting thing is where the pinholes happen--anywhere that the surface> of t=
=3D
he clay had been disturbed in footing--particularly on the rims=3D2C where>=
t=3D
hey get scraped while being centered=3D2C or in the case of berry bowls=3D2=
C in=3D
the area around the holes punched in the base where I've cleaned them up w=
=3D
ith a tool to smooth them. Thus my hypothesis would be that small holes> in=
=3D
the surface of the clay act in a miniscule way like slightly larger holes =
=3D
do--they resist filling with glaze=3D2C and create mini craters in the> gla=
ze=3D
. The other likely place where this would happen would be on the> bottoms w=
=3D
here trimming has occurred=3D2C but I paint slip on those areas after footi=
ng=3D
to avoid pin holing in that area.=3D20
=3D20
It is likely there are strictly glaze related sources of pin holing as well=
=3D
=3D2C but I'm quite sure the surface of the clay plays a role in some pin h=
ol=3D
ing.=3D20
One solution that has worked to avoid the problem has been to paint another=
=3D
no pin holing glaze on in a thin coat in the areas prone to pin holing bef=
=3D
ore dipping it in the susceptible glaze.=3D20
=3D20
Brad Sondahl sondahl.com =3D
Bonnie Staffel on tue 29 may 12
I have two suggestions about eliminating the pinhole problem. I am =3D
thinking
that if one uses a Jiffy Mixer or a machine driven mixer miniscule air
bubbles are created and if there is not enough time lapse to allow these
bubbles to disperse or rise to the top and break, these may be the cause =
=3D
of
the pinholes in the pot. Most all of my problems with pinholes occurred
wherever tooling that was not burnished would result in pinholes. Same =3D
thing
where I attached handles and did not compress the clay at those spots. =3D
My
clay has very fine grog or perhaps other materials that remain hard and =3D
need
to be compressed into the soft clay.=3D20
My second suggestion is that I disagree completely with Tony about using =
=3D
a
sponge to wipe the surface before glazing. Where I have neglected that
operation, pinholes were likely and did appear. There needs to be =3D
surface
tension to be broken and the slightly moist surface handles that. I =3D
don't
mean to soak the pot, but just wipe the surface with a damp sponge. Some =
=3D
of
my potter friends wash their bisque thoroughly the day before the =3D
glazing
session. Here again, it might be important with certain clays only. =3D
Maybe
Tony's clay doesn't require this action so he doesn't have to wipe it. =3D
If
one would want to go this far, it would help immensely if the bisque and
glaze were both warm. If one has a cold studio, the glaze would be cold =3D
and
surface tension would come into play. Most any problems that I found in
working with clay, I would get out my books and look for all possible
solutions or reasons for the fault. However annoying testing might =3D
become,
it is one of the best ways to solve the problem or learn about what is
happening and the steps necessary to take to correct it..=3D20
Sometimes things that seem just natural to a potter, may be the one =3D
thing
that is making the problem. Many times it is just common sense, but if =3D
your
education or experience prepared you for such evaluations, then the =3D
problem
can be easier to solve. When it became necessary for me to handle the 50
pound bags of clay in the studio by myself, leverage came into play, or =3D
I
had to find simpler ways of getting the bag from point A to point B. Now =
=3D
I
have boxes of clay stacked and I use a chair with wheels and gravity to =3D
pull
the box of clay from the stack to land on the seat of the chair as I can =
=3D
no
longer lift or carry such weights. Wheels are my salvation to keep on
working.=3D20
Regards,
Bonnie
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
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