peeling glaze upon application before firing

updated sat 7 jun 03

Paul Lewing on tue 3 jun 03

on 6/3/03 5:49 AM, Derrick Pottery - owner - Wesley Derrick at
verboten@NETDOOR.COM wrote:

> The recipe.(perhaps its makeup is the culprit)
> Magnesium carbonate 37.00 37.00
> Borax 28.00 28.00
> EPK 14.00 14.00
> Lithium carbonate 7.00 7.00
> Colemanite 14.00 14.00
> -------- --------
> Totals: 100.00 100.00
>
> Also add:
>
>
> Copper carbonate 10.00 10.00

Yep, you're right, Wesley- it's the makeup of the glaze that's the problem.
It's the magnesium carbonate. You probably noticed how light and fluffy the
stuff is. Well, it shrinks like mad when it dries. Normally, I'd say to
get your MgO from talc rather than the carbonate, but lots of SiO2 comes
along in the talc, and you don't have any loose silica to take out to
compensate.
Which brings me to your other problems with this glaze, and there are
several. I don't even need to think about running this through a
calculation program to see that this doesn't have anywhere NEAR enough SiO2
to be a durable glaze. Only the EPK and the colemanite are contributing
any, and at that, not much.
Plus, 35% of this glaze, the borax and the lithium carbonate, are soluble.
This will lead to more problems.
To make matters worse, 10% copper carbonate is an ungodly amount of copper.
I don't think I'd have to have this one tested to know that that's not going
to stay in this glaze in any kind of use. I hope you're not even thinking
of getting food anywhere near this stuff, because there's no way this one is
stable.
Paul Lewing, Seattle

Derrick Pottery - owner - Wesley Derrick on tue 3 jun 03

What can be done to remedy the problem of peeling glaze during the
application before firing?

I just made the following recipe over the weekend and have tried brushing
it on a piece 3 times and no matter what thickness, it always peels off the
pot like a sun-soaked mud puddle. The one time that it didn't peel up was
with only (1) coat applied.....but that's not nearly thick enough. It
requires at least (2) coats...but then the cracking starts and then
it peels up.
I haven't had this problem with any other glaze except back in school when
I was dipping instead of brushing and the glaze didn't have enough water
and was too thick with one dip. Easily cured.....but this? I don't know..

The recipe.(perhaps it's makeup is the culprit)
Magnesium carbonate 37.00 37.00
Borax 28.00 28.00
EPK 14.00 14.00
Lithium carbonate 7.00 7.00
Colemanite 14.00 14.00
-------- --------
Totals: 100.00 100.00

Also add:


Copper carbonate 10.00 10.00

Thank You all....
Wesley -- wderrick@sheldonlabs.com
or verboten@netdoor.com

Lois Ruben Aronow on tue 3 jun 03

The problem is the magnesium carbonate, which is used in an extreme
quantity. I am assuming this is a glaze that is meant to crawl, as
most crawling glazes are by nature overloaded with magnesium carb.

This sort of glaze doesn't take well to brushing. If you are
determined to brush, try adding a little cmc - about .25%, and maybe
some veegum. I dip mine, and I have spent the better part of the year
perfecting my handling techniques. =20

Crawling glazes are VERY sensitive to thickness. No matter how thin,
it will probably at least craze on the pot before firing. However,
this kind of glaze needs to be quite thick to get the kind of effects
it is known for, which I am assuming you are after.

I don't know what temp you're firing to, but mine spits like an
orangutan, so get yourself a good kiln wash at the very least.


************
www.loisaronow.com
=46ine Craft Porcelain and Pottery


***************************************
Lois Ruben Aronow
Modern Porcelain and Tableware
http://www.loisaronow.com=20

Derrick Pottery - owner - Wesley Derrick on wed 4 jun 03

Big thanks to you all..
I have been so impressed with the rapport between worldwide potters in this
forum .....it makes my soul very happy to have you all so close via clayart.

..seems the best place for this glaze is not on clay.

I'll play with it a bit this weekend and let those interested no my results
with an update and photos.

I was so curious to see this glaze work because of a '97 post by a lady that
just praised it's results in both her oxidation and reduction (raku)
firings.
Perhaps her post was in reference to the ^6 glaze by the same
name "Moondust" and not the ^06...but with her mention of raku
reduction.....hummm....
Wanted to say....Lois - Ric.....I love y'alls websites...very impressive
work.

In the west nile incubator,
Wesley Derrick
Raymond, MS

william schran on wed 4 jun 03

Wesley wrote: have tried brushing
it on a piece 3 times and no matter what thickness, it always peels off the
pot like a sun-soaked mud puddle.>

The glaze contains 37% magnesium carbonate - that's your problem.

You could sub talc or dolomite for the magnesium, but you'll also
have to adjust the silica with the talc and contend with the calcium
with the dolomite.
Bill