Cindy Hart on thu 14 jul 05
Hi all,
I have mixed up a batch of licorice from Mastering cone 6 glazes and it is
wonderful by itself. My problem is that when I overlap my white glazes on
it the glaze cracks up as it dries and separates in the kiln. I have two
white glazes..
one has gb, epk, silica and superpax. The other is the G1214W with
superpax. I have some students who dipped other glazes (butterscotch and
Variegated Blue)over the black and it did not crack as it dried but it did
separate in the kiln during firing in a spot or two. Carribean Sea Green
and Licorice have no problems.
Ron, if you are reading, can you tell me why this could be happening? It
doesn't happen with any of my other glazes. Is something reacting with the
ingredients in the glaze? I have monitored the thickness and that doesn't
seem to be a problem. We use standard 112 clay. I bisque to ^06 about 13
hours. Glaze fire takes about 8 hours. I am clueless.
Thanks for your help,
Cindy
Cindy Hart on fri 15 jul 05
John,
Thanks for your info. I do overlap within a few minutes however. I wait so
the first glaze won't contaminate the second and then dip relatively
quickly. Licorice is the only glaze this happens with. All the others work
with white and each other fine. Any other ideas why this might be happening?
Thanks,
Cindy
John Hesselberth on fri 15 jul 05
On Thursday, July 14, 2005, at 09:47 AM, Cindy Hart wrote:
> I have mixed up a batch of licorice from Mastering cone 6 glazes and
> it is
> wonderful by itself. My problem is that when I overlap my white
> glazes on
> it the glaze cracks up as it dries and separates in the kiln. I have
> two
> white glazes..
Hi Cindy,
I have found it works best if you put the second glaze on when the
first glaze is just barely dry enough to handle--certainly within a
couple minutes. If the first glaze dries out you can get all kinds of
cracking and separation.
Regards,
John
Ron Roy on tue 19 jul 05
Hi Cindy,
I was doing a glaze course last week so I'm late with this I know.
I can redo the licorice with ball clay and that may do the trick - probably
better to do the glazes that go over the top as well.
Let me know what ball clay you have and send me the white glazes - to
ronroy@ca,inter.net
Sometimes just adding some bentonite to a glaze will help - it tends to
make the surface of each glaze stronger. You would need to test it with a
small batch first though.
RR
>I have mixed up a batch of licorice from Mastering cone 6 glazes and it is
>wonderful by itself. My problem is that when I overlap my white glazes on
>it the glaze cracks up as it dries and separates in the kiln. I have two
>white glazes..
>one has gb, epk, silica and superpax. The other is the G1214W with
>superpax. I have some students who dipped other glazes (butterscotch and
>Variegated Blue)over the black and it did not crack as it dried but it did
>separate in the kiln during firing in a spot or two. Carribean Sea Green
>and Licorice have no problems.
>Ron, if you are reading, can you tell me why this could be happening? It
>doesn't happen with any of my other glazes. Is something reacting with the
>ingredients in the glaze? I have monitored the thickness and that doesn't
>seem to be a problem. We use standard 112 clay. I bisque to ^06 about 13
>hours. Glaze fire takes about 8 hours. I am clueless.
>
>Thanks for your help,
>Cindy
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Cindy Hart on tue 19 jul 05
Hi Ron,
Thanks for your help. The ball clay we have here is OM-4.
The white glazes that we use are:
GB White
Gerstley Borate 50
EPK 17.5
Flint 32.5
G1214W
Flint 25
3134 25
EPK 25
NC-4 Feldspar 15
Wollastonite 10
Both with 10% Superpax.
I looked up the difference between the ball clay and the EPK. It looks like
the ball clay has more silica and less clay than the EPK. Is it too high a
clay content between the glazes that make them crack and separate? I
thought maybe it was the superpax reacting with something at first because
it really only happens with the white glazes and I was going to try and
substitute Zirco or maybe Titanium ($!) to see if that made any difference.
Thanks for your help. I really appreciate your time.
Cindy
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