Hi Everyone, Can glazes go bad? I have a glaze that was real nice when it was new (two years ago). Now it seems to have gone bad. The pots with this glaze on them come out of the kiln with what looks like bubbles that have formed and burst open but never smoothed over. All the other pieces in the same load come out fine with different glazes. I fire to cone 6 oxidation. No matter which clay I use, this particular glaze has been unsuitable lately. It is laguna sage matte. Thanks to anyone answering this question. Sandi
Yes ... over time some ingredients of a glaze can get slowly dissolved in the water. When the glaze is applied to the pot, the dissolved ingredient is absorbed into the clay and out of the glaze mix. Hence, the glaze mix is no longer complete, and all sorts of problems follow.
The solution is to dry the glaze out completely, grind it up and re-mix with water ... or if that's too much trouble, just chuck it out and make a new batch.
Hmm, I'd be really surprised if the dry-and-regrind changed anything. if the problem is solubles. They'll probably redissolve immediately the next time they see water. (They were originally bound to something else in the glaze, but once they have become free salts it will be just as though you had added the salts in the batch.)
But before you pitch the glaze, are you sure that it's completely mixed? It's not uncommon for portions of a glaze to settle out into a "hardpan" layer on the bottom of the container. (Remember, glazes are just suspensions, not solutions, so settling is to be expected.) If this is the case, you may be able to restore it just by some vigorous mixing and sieving. If that doesn't do it, then dry-and-regrind certainly would.
Another way glazes go bad is when there is some organic binder present that deteriorates over time. I think this typically causes a bad odor and/or discoloration, but there are lots of binder products out there so maybe some aren't so obvious when they go bad. At any rate, I don't know if this could cause your symptoms.
Best regards,
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
I am no chemist, so I could well be wrong. Certainly if a frit or other ingredient has broken down into base materials it will be a waste of time.
I understood that some glaze ingredients, although insoluble over the short term, would very slowly dissolve into the water over a long period of time (years). Supposedly these would be reclaimed if the glaze was dried and reconstituted. Dry, regrind and remix was the recommendation from a large premixed glaze manufacturer here in Australia (Cesco) - perhaps this applies to fritted glazes only? I must admit that we have only rarely done this, as the effort usually outweighs the cost of buying or making a new batch.
I am no chemist either, but once the soluble is dissolved in the water, drying out will surely just leave it as a powdered salt. I would not expect it to be re-bound to the original minerals just by drying together with them. What would most assuredly work (if you were stranded on a desert island with only this glaze and your kiln) would be to calcine the whole works into a do-it-yourself frit.
I wouldn't think a properly fritted glaze would ever release anything much into solution... after all, the reason for making a frit in the first place is to make sure those pesky solubles are no more... their metals become part of the glass, and their carbonates, etc, are driven off.
But I agree that it makes a lot more sense to just start over from scratch, in most real-world situations.
Best regards,
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
I was not aware of this. It leads me to ask a question.
I am in the habit of keeping 5 gallons of glaze. When the level in the bucket goes down so much that it is hard to apply through dipping, I mix more and add it in. Is it the case that I am susceptable to this problem? I probably go through 5 gallons of my more popular glazes once a year, but others can take longer.
If you are not having any trouble with your glazes, I wouldn't worry about it - we have glaze mixes ten years old which are still OK. It probably only happens with a small number of ingredients - and in my experience only on low fire glazes.
My understanding is that colemanite (Gerstley borate and the like) is supposed to be infamous for this. I use a lot of this in my glazes and have never noticed a problem, but then I tend to mix small batches.
Solubles tend to be fluxes, so if they go into solution and hence are able to penetrate into the body, then I'd expect the rest of the glaze to have a harder time melting, and maybe look more matte.
Just a thought....
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
I have a blue Raku Glaze which exhibits some interesting behaviour, it contains a mixture of Copper Carbonate and Cobalt Oxide along with a High Alkaline Frit and a bit of china clay. When first mixed and for the first month it is BLUE! From then on it gets progressively more interesting as the Copper starts to act on it. It gets more and more lustrous, and also starts to develop mauves and other subtle hues. However after about 18 to 20 months it suddenly goes haywire, and becomes very matt, black, and a bit like coal clinkers in aspect, so I always make up a new batch when the current one is about 16 months old!
So it would seem on the face of it that flux solubility may well be the reason.
Hi Deer , ...did you fired your pots with bisqwear?or only with fine-gleaze wear?what is the glaze that you re using?bobbles usually apear because of:gases in the kiln , overfireing...and little dotts-uneven glaze coating is usual for a glaze that had seattle for a long time and hedn t been sived so particules have different sizes and they dont melt evenly...that s my experience.Good luck anyway. Red Deer napisal(a):
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