Rod Wuetherick on mon 11 apr 05
Dan,
Why not let the list know what clay body you are using? Perhaps someone on
the list is using it and could share a base that works for you.
There is a lady in my studio that has been having a nightmare getting a blue
celadon to fit on the Silver Falls porcelain body. I suggested we do a
currie grid on it - She got a usable glaze on the first set of tiles. If you
have never taken the time to learn the currie method (volumetric blending) -
I highly reccomend it.
peace,
Rod
Pfeiffer, Dan R (Dan) on mon 11 apr 05
We have been having a problem with stopping crazing in our ^ 10 + base
glaze. We are using a Leach glaze recipe, Custer 40,silica (325)30, Whiting
20,EPK 10 and a bit of Epson salts. The problem is worst in just the base
which we used as a liner on white stoneware (high-water moon). The first
time we used it on test tiles we did not see any crazing so we put it on a
load of pot and lots of crazing. Next we added ~5% more silica and see that
in the glaze that has other oxides in it it looks OK in most places and if
very thin on some pots the clear did not craze, or at least not yet:) So the
question I have is how much silica is too much silica? My guess is if it
starts to shiver you have too much but the reason we are using this is to
get a good balanced glaze, so at what point would this turn into a "bad"
unbalanced glaze?
This is how the firing was done: (gas)
200 deg to 600
250 deg 1100
300 deg ~2300
30 min reduction (.65 oxy) coming up on ^ 10. On cool down we found we ended
up at ^11, we went up too fast but it was getting very late. Next time we
try to come up on 10 slowly and maybe we can prevent the overshoot. We had a
few oil spots we were hoping to improve with the reduction and than a fast
cool down to 2000 and a 1 hour soak. Than closed up and a slow cool down
from there.
The reduction had some very nice effects. The copper greens went pink but
only on one side of ware that was close to a outer shelf edge.Cup edges that
had copper going to clear changed to turquoise and then blue. Cups that were
clear on the reduced side did not craze. The clear does go a bit gray so
maybe the clay body reduced and changed its COE. Very odd! This leads to
more question, will we need to change the silica percentage for each color?
We have been making a large batch of the base and than adding oxides, it
looks like we will need to give this up and make a clear with a high silica
and adjust down based on how the oxides change things. It looks like cobalt
takes the least to stop crazing and copper is only a little better then
clear.
Dan & Laurel in Elkmont
Jonathan Kaplan on mon 11 apr 05
This is a formula for Leach white 40/30/20/10 that I have used
extensively for over 20 years or so with no problems whatsover.
We add 5 % zircopax for a bullet proof white liner and have seen no
evidence of crazing over years of using the glaze, selling our wares
with the glaze(no returns) and hard usage in our home with glazed pots.
I would think its your clay body for which you might add4-7%
pyrophyllite which is a magic good cure for what ails you! You can add
pyrophyllite for parts of the silica/feldspar part of the non-plastics
of the clay proportion.
You firing schedule is a mite too cautious for me, but if it works for
you that's fine.
Send me your clay body formula and I'll have a look at it and change it
for you.
Good Luck!
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139
(please use this address for all USPS deliveries)
Plant Location:
1280 13th Street Suite K
Steamboat Springs CO 80487
(please use this address for all UPS, courier, and common carrier
deliveries only!!)
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
Pfeiffer, Dan R (Dan) on mon 11 apr 05
>>>> Kaplan wrote
You firing schedule is a mite too cautious for me, but if it works for
you that's fine.
Send me your clay body formula and I'll have a look at it and change it
for you. >>>>
You think we could go faster in the firing? I was thinking it was a bit
fast. We are just starting to clear how to fire our own kiln and we are
willing to try anything.
The clay we are using we buy wet so there is not much we can do with it.
Maybe later we will get a pugmill and be able to play that game or go into
mixing dry clay. While it would be fun to do we looked at the time it would
take plus mixer hardware to buy and one more learning curve and decided to
put that one off and just try to get the glaze chemistry down and leave the
clay mixing to others for now. Thanks for the offer!
Dan & Laurel
John Hesselberth on mon 11 apr 05
On Apr 11, 2005, at 12:56 PM, Pfeiffer, Dan R (Dan) wrote:
> ) So the
> question I have is how much silica is too much silica? My guess is if=20=
> it
> starts to shiver you have too much but the reason we are using this is=20=
> to
> get a good balanced glaze, so at what point would this turn into a=20
> "bad"
> unbalanced glaze?
Hi Dan,
This particular glaze is already well balanced with plenty of silica=20
and alumina. While the 5% silica you added won't hurt anything, a=20
better way might be to replace some of the whiting with talc. This will=20=
get both low expansion magnesium (in place of some calcuium) and a=20
little more silica into the mix. I substituted 5% talc for an equal=20
amount of whiting and was able to reduce the expansion quite a=20
bit--more than just adding 5% silica If it still crazes you might go=20
another step or half step. There is usually a bit of space between=20
elimination of crazing and the onset of shivering. Certainly a change=20
per the above shouldn't cause you any trouble.
I have copied the recipes and the unity/expansion numbers in below as=20
info.
Regards,
John
------------------
Recipe Name: Leach 40-30-20-10
Cone: 10 Surface: Color:
Firing: Ox. or Red. Surface:
Amount Ingredient
40 Feldspar--Custer
20 Whiting
10 Kaolin--EPK
30 Silica
100 Total
Unity Oxide
.074 Na2O
.164 K2O
.006 MgO
.756 CaO
1.000 Total
.396 Al2O3
.004 Fe2O3
3.935 SiO2
.001 TiO2
0 P2O5
9.9 Ratio
70.8 Exp
-----------------------------------
---------------------------------------
Recipe Name: Leach 40-30-20-10 -- lower exp
Cone: 10 Surface: Color:
Firing: Ox. or Red. Surface:
Amount Ingredient
40 Feldspar--Custer
15 Whiting
5 Talc
10 Kaolin--EPK
30 Silica
100 Total
Unity Oxide
.077 Na2O
.167 K2O
.149 MgO
.608 CaO
1.000 Total
.404 Al2O3
.004 Fe2O3
4.179 SiO2
.001 TiO2
0 P2O5
10.3 Ratio
67.1 Exp
-----------------------------------
Calculations by GlazeMaster=99
www.masteringglazes.com
------------------------------------
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
scott lykens on mon 11 apr 05
hi dan
i thought the rule of thumb was add silica for crazing subtract it for
peeling.
peeling being the glaze is bigger than the body crazing smaller.
everyhting ive read about crazing has noted it to be most prevelant in high
pot ash glazes and more prevelant in white wares, due to the degree of
kaolinites present in them.
more prevelant in thick clears, dissapting in colored or opcified glazes
ideally keeping free silica to 20% but thats probabbly not realistic
especially if your using a commercial body.
so balancing the silica content between clay body and glaze seems more
realistic.
instead subtracting silica from your glaze I think you should be adding it.
the easy place is by substituting wollastonite for you whiting.
you'll retain the brunt of your calcium while adding a notable amount of
silica.
works fabulous in that old favorite 20/20/20/20/20 cone 6 glaze
of course if opacifers and colorant change the matrix enough to stop it,
save $$$ and keep using your whiting in them.
let me know if im crazy, but please try that test out before ya hollar at
me.
>From: "Pfeiffer, Dan R (Dan)"
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: glazing crazing problem
>Date: Mon, 11 Apr 2005 11:56:44 -0500
>
>We have been having a problem with stopping crazing in our ^ 10 + base
>glaze. We are using a Leach glaze recipe, Custer 40,silica (325)30, Whiting
>20,EPK 10 and a bit of Epson salts. The problem is worst in just the base
>which we used as a liner on white stoneware (high-water moon). The first
>time we used it on test tiles we did not see any crazing so we put it on a
>load of pot and lots of crazing. Next we added ~5% more silica and see that
>in the glaze that has other oxides in it it looks OK in most places and if
>very thin on some pots the clear did not craze, or at least not yet:) So
>the
>question I have is how much silica is too much silica? My guess is if it
>starts to shiver you have too much but the reason we are using this is to
>get a good balanced glaze, so at what point would this turn into a "bad"
>unbalanced glaze?
>
>This is how the firing was done: (gas)
>
>200 deg to 600
>250 deg 1100
>300 deg ~2300
>
>30 min reduction (.65 oxy) coming up on ^ 10. On cool down we found we
>ended
>up at ^11, we went up too fast but it was getting very late. Next time we
>try to come up on 10 slowly and maybe we can prevent the overshoot. We had
>a
>few oil spots we were hoping to improve with the reduction and than a fast
>cool down to 2000 and a 1 hour soak. Than closed up and a slow cool down
>from there.
>
>The reduction had some very nice effects. The copper greens went pink but
>only on one side of ware that was close to a outer shelf edge.Cup edges
>that
>had copper going to clear changed to turquoise and then blue. Cups that
>were
>clear on the reduced side did not craze. The clear does go a bit gray so
>maybe the clay body reduced and changed its COE. Very odd! This leads to
>more question, will we need to change the silica percentage for each color?
>We have been making a large batch of the base and than adding oxides, it
>looks like we will need to give this up and make a clear with a high silica
>and adjust down based on how the oxides change things. It looks like cobalt
>takes the least to stop crazing and copper is only a little better then
>clear.
>
>Dan & Laurel in Elkmont
>
>______________________________________________________________________________
>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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Ron Roy on tue 12 apr 05
Hi Dan,
That glaze would craze on my porcelain unless I added another 10 silica for
instance.
What you want to do is lower the expansion till it stops crazing - for each
type of clay you use.
You can also do it by subbing in some MgO and/or lithium (Spodumene) - not
hard if you have a glaze calculator.
Try the 10% more silica for starters to see if the expansion is low enough
- then experiment with the other ways to get it down.
RR
>We have been having a problem with stopping crazing in our ^ 10 + base
>glaze. We are using a Leach glaze recipe, Custer 40,silica (325)30, Whiting
>20,EPK 10 and a bit of Epson salts. The problem is worst in just the base
>which we used as a liner on white stoneware (high-water moon). The first
>time we used it on test tiles we did not see any crazing so we put it on a
>load of pot and lots of crazing. Next we added ~5% more silica and see that
>in the glaze that has other oxides in it it looks OK in most places and if
>very thin on some pots the clear did not craze, or at least not yet:) So the
>question I have is how much silica is too much silica? My guess is if it
>starts to shiver you have too much but the reason we are using this is to
>get a good balanced glaze, so at what point would this turn into a "bad"
>unbalanced glaze?
>
>This is how the firing was done: (gas)
>
>200 deg to 600
>250 deg 1100
>300 deg ~2300
>
>30 min reduction (.65 oxy) coming up on ^ 10. On cool down we found we ended
>up at ^11, we went up too fast but it was getting very late. Next time we
>try to come up on 10 slowly and maybe we can prevent the overshoot. We had a
>few oil spots we were hoping to improve with the reduction and than a fast
>cool down to 2000 and a 1 hour soak. Than closed up and a slow cool down
>from there.
>
>The reduction had some very nice effects. The copper greens went pink but
>only on one side of ware that was close to a outer shelf edge.Cup edges that
>had copper going to clear changed to turquoise and then blue. Cups that were
>clear on the reduced side did not craze. The clear does go a bit gray so
>maybe the clay body reduced and changed its COE. Very odd! This leads to
>more question, will we need to change the silica percentage for each color?
>We have been making a large batch of the base and than adding oxides, it
>looks like we will need to give this up and make a clear with a high silica
>and adjust down based on how the oxides change things. It looks like cobalt
>takes the least to stop crazing and copper is only a little better then
>clear.
>
>Dan & Laurel in Elkmont
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Pfeiffer, Dan R (Dan) on tue 12 apr 05
>>>>> Rod wrote
Why not let the list know what clay body you are using? Perhaps someone on
the list is using it and could share a base that works for you.
There is a lady in my studio that has been having a nightmare getting a blue
celadon to fit on the Silver Falls porcelain body. I suggested we do a
currie grid on it - She got a usable glaze on the first set of tiles. If you
have never taken the time to learn the currie method (volumetric blending) -
I highly reccomend it.
>>>>>
We are using Highwater's MOON white stoneware. I would like very much to
hear for anyone who is using this clay what they are using.
I am familiar will Currie's method and have make some tile blanks but have
yet to go and do much else with it. It seems that starting will a well know
base I would not need to do more than a small change to the formula and in
our first test tiles it did not look like we need to change anything. Only
in glazing larger ware with different shapes and thickness of glaze did the
problem show up.
so far the best advice from the list on mod's is to replace some whiting
with talc, thanks john, if that does not work I will try replacing what is
left of the whiting with Wollastonite (thanks to Scott's mail). This glaze
does then to bubble a lot so maybe that will improve as well.
Great list I would never have guessed anything other silica.
Dan & Laurel
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