glaze gone bad

On Wed, 4 Oct 2006 06:45:04 +1000, "David Coggins"
wrote:


Hi Everyone,
Can glazes go bad?

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.

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
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

That's quite interesting from my point of view;

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.

Steve
Bath
UK

Snip
In article , Bob Masta
writes

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
Snip
--
Steve Mills
Bath
UK

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):
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