Eleanor on tue 17 aug 04
In a recent post, I mentioned that I fire infrequently which means
that some of my glazes have been stored for a long time--some for two
or three years.
A few of my elderly glazes are not performing as they did when they
were fresh. For example, I have Richard Zakin's New Tyler Amber ^6:
20 Ferro 3110; 60 red clay (Redart); 20 Gerstly Borate which fired to
a shiny dark brown with yellowish speckles as advertised. This glaze
was stored in a plastic Tropicana juice bottle, tightly capped, and
sat on the shelf for a couple of years until I used it to glaze some
mugs. The fired result was shiny and amber-colored--no spots. Some
months later, the glaze in the bottle had become _thin_, watery
although I hadn't added water and had shaken the bottle vigorously.
So I mixed up a new batch and fired. The result was a shiny, darker
amber, attractive, but no spots.
I have another old glaze which used to give interesting surface
effects; now it doesn't. I mixed up a new batch--no help.
These two glazes have an ingredient in common: GB.
Some years ago, when it seemed that Gerstly would no longer be
available, I bought a 50-lb bag of it, which I still have.
I did change clays during this period--from a speckled brown to
Tucker's Smooth White, which may account for the lack of spots in the
Amber glaze but the other glaze in question was used on the white
clay, worked well, and then stopped working.
I store glaze chemicals in covered plastic containers which hold
about ten lbs--not airtight.
Questions: Do glazes have a shelf life? Do glaze chemicals have a shelf life?
Eleanor Kohler
Centerport, NY
Snail Scott on tue 17 aug 04
At 10:53 AM 8/17/2004 -0400, you wrote:
>A few of my elderly glazes are not performing as they did when they
>were fresh...
>These two glazes have an ingredient in common: GB...
Yep, you've got it. Although gerstley borate
is less soluble than borax, it will degrade if
stored for a long time in wet form.
I seldom dip glaze, and usually brush, so I
take advantage of this by not keeping large
amounts of wet glaze on hand. When I mix a large
batch, I keep most of it in reserve as a dry
mix, and only wet as much as I need at a time.
For this glaze, if it's been sitting that long,
write it off, (or call it a new 'limited' glaze,)
and make a fresh batch. At least it didn't have
a pound of cobalt in it! ;)
In the future, if you need enough to dip large
pieces, but only rarely, perhaps you could make a
large batch, then dry it out after glazing and
and crush the chunks, then reconstitute it only
when needed. (I don't actually know if this
would work well enough to be worth the trouble -
just speculating.)
Otherwise, don't make it in quantity until you
know you'll need that much. A five-gallon bucket
is not the only unit of measure, but many folks
will make a 10,000 gram batch every time out of
habit. If a smaller container, or a half-full one,
will do the trick, give it a try. Most glazes
store forever with no trouble, but there's no
advantage to making large batches with soluble
materials if you know it will sit for months or
years. And no sense wasting the last of your
GB that way, either.
-Snail Scott
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