Pamela Regentin on fri 3 oct 03
So, I have this glaze combination I've been successfully using. It is a base glaze that is very stable, doesn't run, etc. and I brush three other glazes in dabs over it. Fired, it has a nice tortoise-shell effect. (Cone 9 oxidation) No problems in the beginning but in the last two or three firings the overglazes are crawling and actually "jumping off" the pot. There are places on the pot that are bare of the three over-glazes but they didn't run off the bottom, they "jumped" off and are lying in puddles on my kiln shelves! ARGH! (or dripped onto other pots, etc.) ARRGHH!! This last firing was worse than the previous. I am suspecting the fit problem is in one over-glaze in particular (a shiny black) because it is crawling when I use it to glaze over the same base glaze, dipped or sprayed on. It only crawls/jumps on the outside of pots, usually the convex curve of a bowl, and the inside will look lovely.
I am wondering if the Alumina hydrate in my kiln wash and also used in my wax (which results in dust on the lid seats after firing) is causing a dust problem in my studio??? Anyone have any ideas? It's so aggravating to have a successful glaze combo mutiny on me.
Other glaze problems...two reliable glazes, used for fifteen years, suddenly started pinholing and blistering like crazy. I can't use them any more. After trying several things (bisque temp changes, different clay bodies, etc.) I've just given up using them and they are great glazes. Someone suggested that the rutile may be contaminated at the mine source. Does anyone know of problems with rutile?
Any helpful input appreciated!
Pam
"But now, O Lord, thou art our father;
we are the clay, and thou our potter;
and we all are the work of thy hand."
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Susan Setley on fri 3 oct 03
In a message dated 10/3/03 5:14:04 AM, clayvessel2@YAHOO.COM writes:
<< Other glaze problems...two reliable glazes, used for fifteen years,
suddenly started pinholing and blistering like crazy. >>
Check the ingredients of your glazes. Maybe the actual content of ingredients
have varied -- started coming from a different mine, for instance.
piedpotterhamelin@COMCAST.NET on fri 3 oct 03
First try brushing off any dust. If you really want to be confident, buy a tack rag from the hardware store and try using this for removing all dust.
If your jumping glaze still gives you problems, mix up some veegum cer ( up to two percent of your batch weight) with water in a blender or hand mixer, screen twice through 80 mesh if like and then add it to your glaze to anchor it down. Perhaps you are loading the kilns and starting the firing with pots that were just glazed and the trapped water in the body is causing the problem.
Perhaps you are using a finer, more plastic or different clay in your mix than you used before and this is causing your premature balding. Calcine the proportion above 10 percent of your clay or up to half of the amount below 10 percent and try this. Maybe you have a hot zone in your kiln and don't realize that you are bisquing higher.
Your pinholes could be resolved by soaking at shut-off time. You could try adding a small amount of a low melt/temp frit to make your glaze more fluid.
Your blisters mean that you are overfiring. Perhaps your pot is too close to the coils if the problem is one sided and facing the side of the kiln.
With both of these glazes, try some fifty gram test of only the base glaze to see if the problem exists with the base or colorants.
Take care
Rick
"Many a wiser men than I hath
gone to pot." 1649
Pamela Regentin on sat 4 oct 03
<mix up some veegum cer ( up to two percent of your
batch weight) with water in a blender or hand
mixer, screen twice through 80 mesh if like and then
add it to your glaze to anchor it down.>>
I'm sorry, I don't know what "veegum cer" is. Do you mean that it will "glue" the glaze to the body? (Like the method of spraying sugar water or Elmer's on a pot). The glaze actually doesn't crawl off the body. Also could the jumping be a flaking at some point in the early firing that would be helped by an adherant?
The glaze combination doesn't show any signs of not sticking to each other, cracking, etc. before firing.
<< Perhaps you are loading the kilns and starting the firing
with pots that were just glazed and the trapped
water in the body is causing the problem.
Perhaps you are using a finer, more plastic or
different clay in your mix than you used before
and this is causing your premature balding. >>>
I wasn't loading wet ware and I was using the same clay, even the same glaze batch. That's why the sudden crawling and worsening of the situation is so strange. Also, the bisque ware was "fresh" and hadn't sat around long getting dusty. The base glaze doesn't crawl off the body but the over-glaze crawls and jumps off the underglaze.
<<< Maybe you have a hot zone in your kiln and
don't realize that you are bisquing higher.
Your pinholes could be resolved by soaking at
shut-off time. You could try adding a small amount
of a low melt/temp frit to make your glaze more
fluid.>>>
It's very possible that a bisque was higher in temp or hot spots, but do I understand incorrectly that a higher bisque temp burns out gases that cause pinholing? Also, both of these particular glazes are very fluid/runny and they look overfired/oversoaked at the same time they have pinholes. That is they have thin spots, high gloss and drips off the bottom. They both have titanium dioxide or rutile also.
<test of only the base glaze to see if the problem
exists with the base or colorants.>>>
A helpful testing tip.
Thanks! Pam
"But now, O Lord, thou art our father;
we are the clay, and thou our potter;
and we all are the work of thy hand."
---------------------------------
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piedpotterhamelin@COMCAST.NET on sat 4 oct 03
It would very much act like a glue but much more effective than sugar. It would keep your glaze in suspension and make mixing easier. Brushing is much easier as well.
Veegum CER is a mixture of Veegum T and medium viscosity sodium carboxymethylcellulose that gives optimum surface hardening of unfired ceramic glazes for safe handling of the ware. It serves as hardener, suspending agent and viscosity stabilizer in glazes.
http://digitalfire.com/material/m-01q1n1.htm
The base glaze doesn't crawl off the body but the over-glaze crawls and
> jumps off the underglaze.
I have seen this happen at about 1400 degrees f in my kilns. Calcining the clay, keeping no more 10 percent plastic and added veegum cer resolved the problem
Clay outgassing improves with a higher bisque with some folks bisquing stoneware pots to cone 04 but a nasty clay could always be troublesome. If you have tried several clays, your glaze is the culprit.
Pinholing could be caused from outgassing of glaze materials as well. Fluorine is bad for this and is found in several frits and Cornwall stone.
Maybe the pots are overfired and the pinholes are actually the start of craters because the glaze is starting to boil. Drop down a cone and see what happens.
You should do a three cone plaque (low, med, high)for your range on each shelf to see the temperature variations in your kiln.
Try glaze samples on different clays as well. Nasty and time consuming but it apparently, must be done.
Good luck
--
"Many a wiser men than I hath
gone to pot." 1649
> <> mix up some veegum cer ( up to two percent of your
> batch weight) with water in a blender or hand
> mixer, screen twice through 80 mesh if like and then
> add it to your glaze to anchor it down.>>
>
> I'm sorry, I don't know what "veegum cer" is. Do you mean that it will "glue"
> the glaze to the body? (Like the method of spraying sugar water or Elmer's on a
> pot). The glaze actually doesn't crawl off the body. Also could the jumping be a
> flaking at some point in the early firing that would be helped by an adherant?
> The glaze combination doesn't show any signs of not sticking to each other,
> cracking, etc. before firing.
>
> << Perhaps you are loading the kilns and starting the firing
> with pots that were just glazed and the trapped
> water in the body is causing the problem.
> Perhaps you are using a finer, more plastic or
> different clay in your mix than you used before
> and this is causing your premature balding. >>>
>
> I wasn't loading wet ware and I was using the same clay, even the same glaze
> batch. That's why the sudden crawling and worsening of the situation is so
> strange. Also, the bisque ware was "fresh" and hadn't sat around long getting
> dusty. The base glaze doesn't crawl off the body but the over-glaze crawls and
> jumps off the underglaze.
>
> <<< Maybe you have a hot zone in your kiln and
> don't realize that you are bisquing higher.
> Your pinholes could be resolved by soaking at
> shut-off time. You could try adding a small amount
> of a low melt/temp frit to make your glaze more
> fluid.>>>
>
> It's very possible that a bisque was higher in temp or hot spots, but do I
> understand incorrectly that a higher bisque temp burns out gases that cause
> pinholing? Also, both of these particular glazes are very fluid/runny and they
> look overfired/oversoaked at the same time they have pinholes. That is they have
> thin spots, high gloss and drips off the bottom. They both have titanium dioxide
> or rutile also.
>
> <> test of only the base glaze to see if the problem
> exists with the base or colorants.>>>
> A helpful testing tip.
> Thanks! Pam
>
>
>
> "But now, O Lord, thou art our father;
> we are the clay, and thou our potter;
> and we all are the work of thy hand."
>
> ---------------------------------
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> The New Yahoo! Shopping - with improved product search
>
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