Greg Lamont on fri 6 jun 97
I have been working with the Chappell's Floating Blue glaze that has gotten
so much press lately in Clayart. I like the glaze except that I am having a
problem with it cracking off the pot in its dry state, and some crawling
when fired. As I recall, the recipe calls for the addition of CMC gum but I
can't seem to find clear instructions on how to use this material. Some
written sources call for mixing a solution of CMC and hot water, but they
don't give proportions of CMC to water, nor do they say how much solution to
add to the glaze. Some clarification would be greatly appreciated.
TIA,
Greg
Ric Swenson on sat 7 jun 97
Carboxymethelcellulose gum CMC , is similar...but different from Gum
Arabic. Used to help the raw glaze surface "harden" and not flake or rub
off the glazed piece. Follow the directions on the package...bag
whatever. Made, I believe, by Hercules Chemical and available at most
ceramic supply stores. I like 7M-2 and 7L type, but there are many
others. CMC gum is used in MANY things....like ice cream! (to make it
smooth...)
R T VanderBilt Co. in Connecticut, makes "Vee Gum Cer" etc... which I
believe contains CMC gum. Conrad Riegger at the lab or someone in sales
there can help you decide which to use.
Mix the powder, WELL with hot water. I think a 50 lb bag makes about 30
gallons?
One percent by volume might be a good spot to start. I used about 10-16 oz
in a 40 gallon batch of glaze.
(It will also help "suspend" the glaze, so it won't "pack down" in the
bucket so much, but a tiny bit of Calcium Chloride works better for that.
Makes the glaze "fluffy". Watch for adding too much chemical "stuff" to
glazes...it can be carried tooooo far.
I used to (many moons ago) use KARO syrup (corn syrup) to give glaze a hard
(sugar crystallized surface?). BUT found the glazes would SOUR after a
while and "Fiendish THINGIES" would grow in the glaze...(unpleasant,
secret grreeeeen things that did not smell well.) It works, but would only
recommend it for glazes that last less than a month.
Experiences of others?
Happy potting!
Uf Da!
Ric Swenson, Bennington
>----------------------------Original message----------------------------
>I have been working with the Chappell's Floating Blue glaze that has gotten
>so much press lately in Clayart. I like the glaze except that I am having a
>problem with it cracking off the pot in its dry state, and some crawling
>when fired. As I recall, the recipe calls for the addition of CMC gum but I
>can't seem to find clear instructions on how to use this material. Some
>written sources call for mixing a solution of CMC and hot water, but they
>don't give proportions of CMC to water, nor do they say how much solution to
>add to the glaze. Some clarification would be greatly appreciated.
>TIA,
>Greg
Ric Swenson, Bennington College, Route 67-A, Bennington, VT 05201-6001 ph
802 442-5401 vox 262 fax 237 direct fax line 802 442-6164 or
email rswenson@bennington.edu
Jeremy/Bonnie Hellman on sun 8 jun 97
Greg-
A while back I posted a query about Chappell's Floating Blue glaze
crawling. I never did get a satisfactory answer (other than the usual
"maybe the bisque was dusty"). However, I have been adding twice as much
cobalt as Chappell's recipe. So I am quite interested to hear that yours
crawls with "only" the called for cobalt.
I have found that I can refire pieces with crawls. I take some of the
thicker glaze (from the sides of the glaze bucket) and just refire. You
do have to watch that the glaze was fully mixed or the color doesn't
quite blend in.
Chappell discusses how to add CMC in his book, but I don't mix it in
water first and measure it out by the teaspoonful as he says. I just add
it with my dry ingredients when I am measuring. Then I add water to the
whole mix, sieve and use. I've been experimenting with an approriate
percentage but my notes are elsewhere from this computer so I can't tell
you at this time what I used last. If you are not satisfied with the
answers you get from other people, let me know and I'll dig up what I
used last--because it's working fine. I made 8,000 grams which will last
me quite a while, and just don't remember what I used.
Bonnie Hellman in Pittsburgh, PA
>----------------------------Original message----------------------------
>I have been working with the Chappell's Floating Blue glaze that has gotten
>so much press lately in Clayart. I like the glaze except that I am having a
>problem with it cracking off the pot in its dry state, and some crawling
>when fired. As I recall, the recipe calls for the addition of CMC gum but I
>can't seem to find clear instructions on how to use this material. Some
>written sources call for mixing a solution of CMC and hot water, but they
>don't give proportions of CMC to water, nor do they say how much solution to
>add to the glaze. Some clarification would be greatly appreciated.
>TIA,
>Greg
From University of California Professor Robert Silensky:
"We've all heard that a million monkeys banging on a million typewriters
will
eventually reproduce the entire works of Shakespeare. Now, thanks to the
Internet, we know this is not true."
Martin Schiller on sun 8 jun 97
>Mix the powder, WELL with hot water. I think a 50 lb bag makes about 30
>gallons?
>
>One percent by volume might be a good spot to start. I used about 10-16 oz
>in a 40 gallon batch of glaze.
>Experiences of others?
If memory serves I didn't use very much of the powder at all - perhaps a
tablespoon for a 10 pound batch of glaze. But it was a long time ago and
I only suggest it as a starting point because I remember being amazed
that such a small amount of material would have such a dramatic effect.
The thing that I'm sure of is that I discovered CMC would dissolve almost
immediately in alcohol (rubbing, denatured) and could be mixed and added
to a glaze quickly and relatively simply.
If you are experimenting, you might try mixing your glaze and then
dissolving two or three tablespoons of CMC in a cup of alcohol and then
stirring the dissolved mix into your glaze. Again, memory dims, but I
seem to remember that I needed to adjust the water content of the glaze
after adding the CMC. Try adding the dissolved CMC while stirring until
you notice a change in viscosity, and see how that amount works. You
should be able to add more later,if it seems needed.
warm regards,
Martin.
Jim Horvitz on mon 9 jun 97
To prepare a glaze with a small amount of CMC-dry blend all the ingrediants
before adding water. The hydrophylic colloids go into sollution more easily
if they are dispersed this way. Most water loving colloids go into solution
easier in hot water---Methylcellulose is the exception it desolves in cool
water faster. Jim Horvitz Rancho Mirage CA
David W Gordon on mon 9 jun 97
I've been mixing 25 grams to a quart of water, putting it through a
blender, and using 1 teaspoon per 100 grams of glaze (approx 1 cup for a
5 kilogram batch). Seems to work well with this glaze as far as getting
rid of the cracking problem, the crawling is another story.
David W. Gordon dwgordon@tenet.edu
San Antonio, Tx.
On Fri, 6 Jun 1997, Greg Lamont wrote:
> ----------------------------Original message----------------------------
> I have been working with the Chappell's Floating Blue glaze that has gotten
> so much press lately in Clayart. I like the glaze except that I am having a
> problem with it cracking off the pot in its dry state, and some crawling
> when fired. As I recall, the recipe calls for the addition of CMC gum but I
> can't seem to find clear instructions on how to use this material. Some
> written sources call for mixing a solution of CMC and hot water, but they
> don't give proportions of CMC to water, nor do they say how much solution to
> add to the glaze. Some clarification would be greatly appreciated.
> TIA,
> Greg
>
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