Susan Ross on fri 2 apr 99
I buy dry-mixed Laguna ^5 glazes, add a recommended amount of bentonite to
them for dipping at 55 on the hydrometer. This quarter we've had major
problems with a number of the glazes peeling up off each other or up off the
pots as they dry after dipping and/or pouring. An annoying problem to say the
least since we generally end up with bald spots or crawling on our pots.
I've run a couple of tests: making sure the pot is clean, not greasy or waxy;
making sure the first glaze is completely dry before pouring anything on top
of it. What else might be the problem? Maybe too much bentonite?
TIA
Susan Ross
Piedmont Clay Studio
Piedmont, CA
Chris Schafale on sun 4 apr 99
Susan,
This is a problem I've been having *a lot* in the last several
months, though not with pre-mixed glazes. I'll say up front that I
don't know the answer, but I thought of some questions for you to
consider:
Did the problem start when you mixed a new batch of glaze from a
new supply of dry-mixed glaze? If so, go on, if not, I'm clueless.
Do you still have some buckets of glaze that have not had new
materials added and are behaving OK? If so, it may halp to make some
comparisons, based on the questions below:
Does the problem glaze appear normal in thickness and viscosity,
compared to how it used to look or compared to other glazes you are
using? Does it apply in the same way as it used to, or does it tend
to form thick drips you can't shake off the pot? (My problem glazes
appear somewhat thickened, and have application problems indicating
too much viscosity). Stick a dry finger in the glaze and see how
many drips come off ( mine don't drip at all.) Compare this to
other glazes that are working OK.
Do you measure specific gravity with a hydrometer, and if so, have
you checked it against a weighed sample (measure 100 ml/cc carefully,
weigh it, and divide by 100 -- the result is your specific gravity
reading). In my situation, I discovered that the hydrometer readings
for the problem glazes were way off, because of the viscosity
described above. I had a lot more water in my glaze (lower s.g.)
than you ever would have thought based on appearance and "feel".
More water means more shrinkage, which can lead to the
cracking/peeling problems you describe.
Have you talked to Laguna about this? I still haven't figured out
what my problem is, but it's an interesting coincidence that my
similar problems began with materials I bought last fall, that came
from Laguna. I've had some suspicions about the possibility of a bad
batch of EPK, and if they are using EPK in the glazes they are
mixing, hmm....
Advice I've gotten from some of the glaze gurus suggests that my
problem glazes are probably flocculated so they take excess water to
make them fluid. Now I'm trying to get rid of the extra water and
then working with Darvan 7 to try to get them de-flocculated and see
if that helps. So far, I've had some success getting them to flow,
but they still crack.
Best of luck, and I hope your problem turns out to be something
simple and fix-able.
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@intrex.net
| |
|
