Judy Rohrbaugh on thu 8 sep 05
I made up a new glaze that I apply fairly thinly underneath another glaze that I have used for years to get an aqua blue color. I have been using these two glazes together for the past 6 months.
Everything within reason has been going fine until the last two firings. I have been getting pots that have severe crawling. Glaze has fallen off the pots and this morning I have three ruined kiln shelves. ( They haven't been washed in 3 years as I never have problems!)
At first I thought the second glaze was on too thinly, but that's not the cause. The underneath glaze is not too reliable alone, it does crawl in spots if it is applied alone.
The only thing I have done differently is fire perhaps just a bit faster, as there were none of my "extra" fragile pots in the kiln. Kiln fired in about 10 1/2 hours instead of 12.
The top glaze has about 1% copper, under glaze has about 1% cobalt. Both have Gillespie borate in the base, and very basic ingredients.
Also, I guess my shelves are ruined? Nothing I can temporarily put overtop the glaze splotches?
Thank you,
Judy Rohrbaugh
Fine Art Stoneware
Ohio, USA
Judy Rohrbaugh on thu 8 sep 05
I looked at my kiln log---These two loads were fired the usual time, not faster. Too many loads , it all blends together.
Judy Rohrbaugh
Judy Rohrbaugh wrote:
I made up a new glaze that I apply fairly thinly underneath another glaze that I have used for years to get an aqua blue color. I have been using these two glazes together for the past 6 months.
Everything within reason has been going fine until the last two firings. I have been getting pots that have severe crawling. Glaze has fallen off the pots and this morning I have three ruined kiln shelves. ( They haven't been washed in 3 years as I never have problems!)
At first I thought the second glaze was on too thinly, but that's not the cause. The underneath glaze is not too reliable alone, it does crawl in spots if it is applied alone.
The only thing I have done differently is fire perhaps just a bit faster, as there were none of my "extra" fragile pots in the kiln. Kiln fired in about 10 1/2 hours instead of 12.
The top glaze has about 1% copper, under glaze has about 1% cobalt. Both have Gillespie borate in the base, and very basic ingredients.
Also, I guess my shelves are ruined? Nothing I can temporarily put overtop the glaze splotches?
Thank you,
Judy Rohrbaugh
Fine Art Stoneware
Ohio, USA
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Marcia Selsor on thu 8 sep 05
Judy,
I don't know what happened to your glazes but you should be able to
get most of the glaze off your shelves with a cold chisel and then
grinder. Wear safety goggles.
I have cleaned lots of shelves in the classroom situation. Then put a
good layer of kiln wash onto the top surface of the shelf. Make sure
you have the glaze off completely. It will come back to haunt you if
you don't.
Marcia Selsor
On Sep 8, 2005, at 6:20 AM, Judy Rohrbaugh wrote:
> I made up a new glaze that I apply fairly thinly underneath
> another glaze that I have used for years to get an aqua blue
> color. I have been using these two glazes together for the past 6
> months.
>
> Everything within reason has been going fine until the last two
> firings. I have been getting pots that have severe crawling.
> Glaze has fallen off the pots and this morning I have three ruined
> kiln shelves. ( They haven't been washed in 3 years as I never
> have problems!)
>
> At first I thought the second glaze was on too thinly, but that's
> not the cause. The underneath glaze is not too reliable alone, it
> does crawl in spots if it is applied alone.
>
> The only thing I have done differently is fire perhaps just a bit
> faster, as there were none of my "extra" fragile pots in the kiln.
> Kiln fired in about 10 1/2 hours instead of 12.
>
> The top glaze has about 1% copper, under glaze has about 1%
> cobalt. Both have Gillespie borate in the base, and very basic
> ingredients.
>
> Also, I guess my shelves are ruined? Nothing I can temporarily put
> overtop the glaze splotches?
>
> Thank you,
> Judy Rohrbaugh
> Fine Art Stoneware
> Ohio, USA
William & Susan Schran User on thu 8 sep 05
On 9/8/05 8:20 AM, "Judy Rohrbaugh" wrote:
> The only thing I have done differently is fire perhaps just a bit faster
Are you certain this is the only thing you have done differently?
I don't think a change from 12 hours to 10 1/2 hours would cause your
crawling issues, unless the start of the firing was much faster than usual.
The one thing that comes to mind is that the glaze/clay had not dried
sufficiently prior to firing. Did you fire soon after glazing?
Did you open a new bag of any of the glaze ingredients when you mixed the
glazes?
The glaze will be tough to get out of the shelves. You'll probably end up
removing quite a number of chinks of shelf with the glaze drips.
Don't understand you question about " Nothing I can temporarily put overtop
the glaze splotches?" Certainly you can fill the voids with glaze and
re-fire, but unless they are major works, you might be better off trashing
them and chalk this up to a learning experience.
--
William "Bill" Schran
Fredericksburg, Virginia
Alyssa Ettinger on thu 8 sep 05
judy, i can't tell you about the scientifics about the glaze. but, do have
some advice on the shelves: a dremel. if you don't have one they're an
invaluable investment (i fire on my communal studios cruddy shelves, so i
always need to get something or other off the feet of my pots).
i don't know how much glaze you can get off, but a whole lot. and then
likely use the polishing tool to smooth out the rough patches. will take
some work, and will never be perfect... but will save the cost of new kiln
shelves.
alyssa
www.alyssaettinger.com
Judy Rohrbaugh on thu 8 sep 05
Thanks, I am eagerly reading these responses, as this has never happened before-that's why I don't bother with the kiln washing.
So, far, I would say the idea about pots being too damp sounds possible, as I am putting two layers of glaze on, and my pots are not very thick. A few pots came out ok, but many did not. I don't keep track, but there were some that I put the first layer on, and 8 hours later, the second layer. Others I did both layers in the same day.
I often do two layers of glaze, but they are usually only on part of the piece. These pots are completely covered with both glazes, making for what I thought was a nice mottling.
William
When I was talking about putting something over the glaze splotches, I meant on the shelves, at least temporarily, not the pots. (Laughing.) The pots are in the trash.
Judy Rohrbaugh
Ohio
William & Susan Schran User wrote:
Don't understand you question about " Nothing I can temporarily put overtop
the glaze splotches?" Certainly you can fill the voids with glaze and
re-fire, but unless they are major works, you might be better off trashing
them and chalk this up to a learning experience.
--
William "Bill" Schran
Fredericksburg, Virginia
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Ann Brink on thu 8 sep 05
Hello Judy,
I don't know the size and depth of the glaze splotches, but yes, you might
want to try a coating of the kiln wash I use which is 50/50 alumina hydrate
& EPK. There have been a few areas on my shelves where I couldn't entirely
clean off glaze drips, so I ground the area smooth, applied kiln wash and
used them. The wash seems to sort of "absorb" the glaze. Check the areas
after each firing- if the glaze is becoming visible, add more kiln wash.
Good luck!
If your glaze drips are so bad you have an uneven surface, you could use
thin cookies under your pieces (but put grog, etc under them so they don't
get stuck)
Ann Brink in Lompoc CA
> Also, I guess my shelves are ruined? Nothing I can temporarily put
overtop the glaze splotches?
>
> Thank you,
> Judy Rohrbaugh
> Fine Art Stoneware
> Ohio, USA
>
William & Susan Schran User on thu 8 sep 05
On 9/8/05 11:19 AM, "Judy Rohrbaugh" wrote:
> When I was talking about putting something over the glaze splotches, I meant
> on the shelves, at least temporarily, not the pots.
Judy - As others have written, you will need to remove all glaze from the
shelf. Any remaining glaze that is in the shelf will continue to melt each
firing, making it even worse.
Chiseling, grinding, whatever it takes - make sure you wear proper lung &
eye protection.
Had a major glaze-on-shelf issue. Crystalline glaze, catch basin split,
much, much glaze through wash into shelf. Almost had to chisel all the way
through the shelf. Filled the hole/divot with mix of alumina/kaolin/mullite
and covered with kiln wash - seems to work.
--
William "Bill" Schran
Fredericksburg, Virginia
Jim Willett on thu 8 sep 05
Judy,
We do a lot of "double dipping". Glaze over glaze. We have found two
things very important to preventing glaze crawling. First we allow the
glazes to dry thoroughly (over night if possible) before firing, and second
we ramp up very slowly (20 to 60 degrees an hour) and hold at 190 for two or
three hours to allow all the moisture to slowly leave the glaze. Only then
do we ramp on up. Only when we try to "push" do we run into problems.
Sometimes just more humid weather is all it takes to cause problems. Hope
this helps.
Jim and Cindy
Out of the Fire Studio
Edmonton, Alberta, Canada
http://www.outofthefirestudio.com
http://potblog.outofthefirestudio.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Judy Rohrbaugh
Sent: Thursday, September 08, 2005 6:20 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: severe crawling with cone 6 glazes
I made up a new glaze that I apply fairly thinly underneath another glaze
that I have used for years to get an aqua blue color. I have been using
these two glazes together for the past 6 months.
Everything within reason has been going fine until the last two firings. I
have been getting pots that have severe crawling. Glaze has fallen off the
pots......
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__
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Judy Rohrbaugh on fri 9 sep 05
Thank you everyone for all of the help with my glaze crawling problem.
William, I believe you were right when you asked "are you sure you didn't do anything different?" The small thing that I did differently was to glaze this groups of pots *last*, even though they go into the kiln first. I normally have only a few of these, and glaze these first, put them into the kiln, clean up and change colors and do the rest of the load. So until these past two loads they would have had another day or two to dry.
I often glaze pieces with threee or four dips, and wait overnight before I put on the last small dip.
So, I think it was too much moisture.
I also think my 6 month batch, which I have added more to, may be now a bit soluble.
So, I will mix a fresh batch of the new glaze and test first.
Also, thank you to everyone about the kiln shelf advice. Of course this is happening when I need to keep firing and working!
Wish I would have asked this question after I had problems with the first load, which were less severe (no shelf damage yet. ) Oh, well.
Judy Rohrbaugh
Fine Art Stoneware
Ohio
Ron Roy on fri 9 sep 05
Hi Judy,
Send me the recipe of both glazes - it may be possible to revise one or
both to help cure the problem.
It may be that the GB sub is flocculating the slop - it can be replaced
with a frit - which will eliminate the problems brought on by solubles.
RR
>I made up a new glaze that I apply fairly thinly underneath another glaze
>that I have used for years to get an aqua blue color. I have been using
>these two glazes together for the past 6 months.
>
>Everything within reason has been going fine until the last two firings.
>I have been getting pots that have severe crawling. Glaze has fallen off
>the pots and this morning I have three ruined kiln shelves. ( They
>haven't been washed in 3 years as I never have problems!)
>
>At first I thought the second glaze was on too thinly, but that's not the
>cause. The underneath glaze is not too reliable alone, it does crawl in
>spots if it is applied alone.
>
>The only thing I have done differently is fire perhaps just a bit faster,
>as there were none of my "extra" fragile pots in the kiln. Kiln fired in
>about 10 1/2 hours instead of 12.
>
>The top glaze has about 1% copper, under glaze has about 1% cobalt. Both
>have Gillespie borate in the base, and very basic ingredients.
>
>Also, I guess my shelves are ruined? Nothing I can temporarily put
>overtop the glaze splotches?
>
>Thank you,
>Judy Rohrbaugh
>Fine Art Stoneware
>Ohio, USA
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Judy Rohrbaugh on fri 9 sep 05
Ron, and anyone else,
Here is the glaze that I used underneath. This is not what I consider a good stable glaze to use alone, it's shiny and gives a bright color, so I have used it in spots under and over other glazes of similar color to punch it up a bit.
This is the original glaze I used years ago at cone 4, oxidation. (not currently using)
I used to have to keep this dry and mix only as needed, I wondered if that is still my problem even revised:
Feldspar- 47
flint- 20
whiting-8
colemanite- 14
zn oxide- 4
dolomite-6
used with small amounts of copper for turquoise, also with iron ox 3% and manganes 2.5% for a straw yellow.
also small amounts of copper and iron ox together make a strong green (did not keep the notes)
REVISED CURRENT GLAZE:
This is the current glaze that I started to use 6 months ago as a blue, underneath a turquise blue, to brighten it up and get it more blue and mottled:
This time it is at cone 6:
Current glaze:
Ball clay 12
feldspar-30
flint-30
whiting-8
gillespie borate- 6
zn oxide- 4
dolomite- 6
bentonite-1
If anyone does bother with this and gets any neat results I would love to know. Remember, at least for me, it is a "touchy" not very reliable glaze used alone. And the last time, it fell off my pots.
Judy Rohrbaugh
Fine Art Stoneware
Ohio
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Ron Roy on sun 11 sep 05
Hi Judy,
I calculated the 2nd glaze out and really can't see why it would fall off.
Zinc oxide that is not calcined can do a lot of shrinking but aside from
that - and maybe the gillespie borate - there is nothing I would suspect.
The recipe only totals 97.0 by the way - anything left out?
Could it be that you mixed up a new batch and made a mistake? I think not
because you have used this batch before - right?
Anyway I have reformulated it - reduced the ZnO and upped the ball clay and
bentonite - worth a try - maybe mix 500 grams to see if it sticks.
You may also want to consider some pure water like Deionized or distilled -
local waters can and do change and contribute to problems.
OM #4 - 15.0 ( I calculated using OM - are you using something else?
Custer - 26.0 (you using Custer?)
Silica - 32.0
Whiting - 9.0
Gil Borate - 7.5
Zinc ox - 2.0
Dolomite - 8.5
Bentonite - 2.0
Total - 102.0
Hope this helps - RR
>Here is the glaze that I used underneath. This is not what I consider a
>good stable glaze to use alone, it's shiny and gives a bright color, so I
>have used it in spots under and over other glazes of similar color to
>punch it up a bit.
>
>This is the original glaze I used years ago at cone 4, oxidation. (not
>currently using)
> I used to have to keep this dry and mix only as needed, I wondered if
>that is still my problem even revised:
>
>Feldspar- 47
>flint- 20
>whiting-8
>colemanite- 14
>zn oxide- 4
>dolomite-6
>
>used with small amounts of copper for turquoise, also with iron ox 3% and
>manganes 2.5% for a straw yellow.
>also small amounts of copper and iron ox together make a strong green (did
>not keep the notes)
>
>REVISED CURRENT GLAZE:
>This is the current glaze that I started to use 6 months ago as a blue,
>underneath a turquise blue, to brighten it up and get it more blue and
>mottled:
>This time it is at cone 6:
>
>Current glaze:
>
>Ball clay 12
>feldspar-30
>flint-30
>whiting-8
>gillespie borate- 6
>zn oxide- 4
>dolomite- 6
>bentonite-1
>
>If anyone does bother with this and gets any neat results I would love to
>know. Remember, at least for me, it is a "touchy" not very reliable glaze
>used alone. And the last time, it fell off my pots.
>
>
>Judy Rohrbaugh
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Judy Rohrbaugh on mon 12 sep 05
Ron,
Thank you for calculating my glaze. 97 is correct, this glaze fired originally at cone 4 and I reworked it.
I use Ky om4 ball and Feldspar is NC-4.
From the advice I have gotten from clayart, and my own suspicions, I think the pots were too wet. I also think the glaze may have become a bit soluble. That combined with the fact that I glazed these pots last instead of first, they had 24-48 hours less time to dry out.
And since you think the glaze looks ok, I will be mixing another small batch up today and trying it again on a few pots.
I am in the middle of a three weekend show, so I have to just keep glazing for now.
After the show is over I will have some time to test, so I will try your version. And, of course if it's better, I will use that one.
I will let you know how it turns out.
Judy Rohrbaugh
Fine Art Stoneware
Ohio
Ron Roy wrote:
Hi Judy,
I calculated the 2nd glaze out and really can't see why it would fall off.
Zinc oxide that is not calcined can do a lot of shrinking but aside from
that - and maybe the gillespie borate - there is nothing I would suspect.
The recipe only totals 97.0 by the way - anything left out?
Could it be that you mixed up a new batch and made a mistake? I think not
because you have used this batch before - right?
Anyway I have reformulated it - reduced the ZnO and upped the ball clay and
bentonite - worth a try - maybe mix 500 grams to see if it sticks.
You may also want to consider some pure water like Deionized or distilled -
local waters can and do change and contribute to problems.
OM #4 - 15.0 ( I calculated using OM - are you using something else?
Custer - 26.0 (you using Custer?)
Silica - 32.0
Whiting - 9.0
Gil Borate - 7.5
Zinc ox - 2.0
Dolomite - 8.5
Bentonite - 2.0
Total - 102.0
Hope this helps - RR
>Here is the glaze that I used underneath. This is not what I consider a
>good stable glaze to use alone, it's shiny and gives a bright color, so I
>have used it in spots under and over other glazes of similar color to
>punch it up a bit.
>
>This is the original glaze I used years ago at cone 4, oxidation. (not
>currently using)
> I used to have to keep this dry and mix only as needed, I wondered if
>that is still my problem even revised:
>
>Feldspar- 47
>flint- 20
>whiting-8
>colemanite- 14
>zn oxide- 4
>dolomite-6
>
>used with small amounts of copper for turquoise, also with iron ox 3% and
>manganes 2.5% for a straw yellow.
>also small amounts of copper and iron ox together make a strong green (did
>not keep the notes)
>
>REVISED CURRENT GLAZE:
>This is the current glaze that I started to use 6 months ago as a blue,
>underneath a turquise blue, to brighten it up and get it more blue and
>mottled:
>This time it is at cone 6:
>
>Current glaze:
>
>Ball clay 12
>feldspar-30
>flint-30
>whiting-8
>gillespie borate- 6
>zn oxide- 4
>dolomite- 6
>bentonite-1
>
>If anyone does bother with this and gets any neat results I would love to
>know. Remember, at least for me, it is a "touchy" not very reliable glaze
>used alone. And the last time, it fell off my pots.
>
>
>Judy Rohrbaugh
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.
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