Lois Ruben Aronow on fri 3 mar 00
------------------
I have been using this nifty green for a while on my own work with
much success. I was thinking of making it as a studio glaze, but
don't want to until I can make it stop crazing. It's a really
wonderful green with red specs in it, reacts differently on buff
stoneware, white stoneware, and porcelain. How can I make the crazing
go away without altering the great character of this glaze?
Oh yeah - =5E6 Ox
Neph Sy 67
Dolomite 10
Kaolin 8
Silica 9
Zinc Ox 6
Add:
Copper carb 3
Bentonite 1
thanks
Lois Ruben Aronow
=2A=2A=2A=2A=2A=2A=2A
gilois=40earthlink.net
David Hewitt on sun 5 mar 00
Hello Lois,
I think you have a problem here. I calculate that your recipe has a
coefficient of expansion of 6.04 x10-6/oC linear English & Turner. In my
experience it is not surprising that you are having crazing. You
probably have an excellent decorative glaze where crazing can be used to
advantage. Would I be correct in guessing that the crazing is greatest
on the porcelain body?
I would think, therefore, that to correct the crazing would require a
fairly radical change and hence it could well change the colouring
effect that you like.
One possible change that reduces the calculated coefficient of expansion
to 4.11 x10-6/oC linear is as follows:
reduce the Neph Sy to 35
increase the kaolin to 15
increase the silica to 40
add lithium carb. 5
The above is a 'paper' exercise and would obviously need to be tested.
David
In message , Lois Ruben Aronow writes
>----------------------------Original message----------------------------
>------------------
>I have been using this nifty green for a while on my own work with
>much success. I was thinking of making it as a studio glaze, but
>don't want to until I can make it stop crazing. It's a really
>wonderful green with red specs in it, reacts differently on buff
>stoneware, white stoneware, and porcelain. How can I make the crazing
>go away without altering the great character of this glaze?
>
>Oh yeah - =5E6 Ox
>
>Neph Sy 67
>Dolomite 10
>Kaolin 8
>Silica 9
>Zinc Ox 6
>
>Add:
>Copper carb 3
>Bentonite 1
>
>thanks
>Lois Ruben Aronow
> =2A=2A=2A=2A=2A=2A=2A
>gilois=40earthlink.net
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Ron Roy on mon 6 mar 00
Hi Lois - try this.
Mis up 500 grams of your original and 500 of this revision - I have lowered
the the expansion a lot - after you have dipped tests in thos - mix them
together - the middle one will have expansion between your original and my
revision.
I don't know if they will all look the same - probably not - and some times
even better.
Neph Sy - 42.5
Dolomite - 13.5
EPK - 21.5 << probably you will not need the bentonite in this one)
Silica - 16.0
Zinc oxide - 6.5
Total - 100.0
Ratio - 4.88 (original is 4.86)
Expansion - 488.74 (original is 598.14)
The next step in this attempt to tame a glaze is to replace the Neph Sy
with G200 or Custer but it must be done by calculation in order to get all
the oxides balanced.
Let us know what happens please.
RR
>----------------------------Original message----------------------------
>I have been using this nifty green for a while on my own work with
>much success. I was thinking of making it as a studio glaze, but
>don't want to until I can make it stop crazing. It's a really
>wonderful green with red specs in it, reacts differently on buff
>stoneware, white stoneware, and porcelain. How can I make the crazing
>go away without altering the great character of this glaze?
>
>Oh yeah - ^6 Ox
>
>Neph Sy 67
>Dolomite 10
>Kaolin 8
>Silica 9
>Zinc Ox 6
>
>Add:
>Copper carb 3
>Bentonite 1
>
>thanks
>Lois Ruben Aronow
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
S.E.W. on mon 29 nov 04
Sherri
I have used commercially prepared slip/clay and I always have used =
Duncan Infinity Clear glaze and I have NOT had the problems that =
everyone seems to think arise due to using commercial products. I would =
start at the bottom and narrow the first possible problem which is the =
kiln and checking that it is reaching the proper cone. If that is o.k., =
then I would change the clay or the glaze, but not both at the same =
time. Do you use other glazes and if so, do they craze? If not, then =
don't change the clay body, change the glaze.=20
Also, you mentioned using porcelain and then firing the glaze at 04-06? =
I would check up on that. I don't know about using low fire glazes on =
high fire clay bodies. I have had crazing when I over fired my clear =
glaze. I learned to never fire your clear above 06.=20
Rachel
S.E.W. on mon 29 nov 04
Sherri,
The first thing I would suggest is to make sure your kiln is =
reaching the proper cone. If your piece (bisque) is underfired in the =
first place and then you apply glazes, there will be all kinds of =
problems, including crazing. I would check that before changing the =
clay and glazes you use. Making sure you reach the proper cone is very =
important! Check that and let me know! Also, fire your bisque to a cone =
hotter, like 03. It sounds like your problem isn't the clay body or =
glaze, especially if you have changed them many times. When you fire =
next time, use a couple witness cones and place them on each shelf of =
the kiln. If you are firing to 04, place an 03, 04, and 05 witness cone =
on each shelf and you will be able to tell if the kiln is under or even =
over firing. Also, by placing them on each shelf, you can tell if =
certain areas of the kiln are having problems.=20
Rachel
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