bonnie staffel on mon 4 apr 05
Well, guys and gals, and Bill Edwards, here I go again. Mixing CMC with
COLD water is really a no-no in common sense or you will have a mess on your
hands. A method that has worked extremely well for me is when you use it
dry, blend it in some OTHER DRY INGREDIENT of your glaze and then add your
glaze ingredients to HOT water. I have found that 1/2 of one percent works
well with most glazes. Use less water than you normally might need for your
glaze. After screening a couple of times, it should be ready for use. I
use a hydrometer to get it to the proper dipping mixture for your bisque
absorbency. You will find that it will react quite quickly.
On the other hand, if you want to make a brushing solution, take an old
Waring type blender that is used for nothing else, add HOT water to the jar
about half way full, turn it on and very slowly add less than a quarter cup
of dry CMC or maybe only 2 tablespoons depending on how thick you want the
mixture. Let it whirl until it is all mixed. You will have a gum solution
immediately.
I have added this gum solution in the early days of my career but felt that
it was not measurable in the quantity of glaze I was mixing, so found the
result frustrating.
Something you should learn in Clay 101, is that if you add dry clay or glaze
materials to water, they slake much faster if you add them to HOT water.
HOT water has less surface tension.
When adding Bentonite to your glaze mixing process, also dry mix the amount
of bentonite, usually 1 or 2 percent, with one of the dry ingredients before
putting in into the water.
These methods have not failed me for many years, probably longer than some
of you are old!!!! I changed the subject so that this post can be easily
retrieved from the archives.
Warm regards,
Bonnie Staffel where the sun is shining but I have caught the bug you all
enjoyed in Baltimore.
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
Charter Member Potters Council
URL Krueger on mon 4 apr 05
To add to, and maybe clarify, the excellent comments made by
others.
Many times we think of chemical processes as taking place
instantaneously. This is often not the case. Some process
take considerable time to complete and the hydration of CMC
is one of those. The advantage of using hot water is that
the heat speeds up the hydration process. What may take
1/2 hour with hot water may take a day with cold.
CMC consists of long molecules of cellulose, just as you
find in paper or cotton, that have been chemically modified
to produce a substance with different properties. Most of
the desirable properties of CMC, such as high viscosity,
are dependent on these long molecules. When you use a high
shear mixer, such as a blender, you break these long
molecules into shorter pieces and thus lose the properties
you are looking for. This explains why blended CMC has a
lower viscosity then unblended.
--
Earl K...
Bothell WA, USA
An ex-chemist who used CMC in a totally different way.
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