I got the recipe I had heard about from Walter Lieberman. Walter does some wonderful glass painting. His website is
http://web.media.mit.edu/%7Elieber/Walt/
"This is how I made the pastels,You get Gum Tragacanth( this a natural
resin gum not unlike gum arabic). This is the traditional binder for
pastels. You can get it at good art stores or you can order it from
one of the nationally famous ones like Pearl Paints in NYC, or Kremer
Pigments in NYC
http://www.kremer-pigmente.de/englisch/homee.htm
. It comes as a powder you soak it in water overnight, I forget how
much I don't think it matters. Stir it up and strain out any
undissolved gum. Mix your enamel with just enough water to make a
paste. Add a few drops of your gum solution. Knead the mixture till
it becomes like putty. Roll out individual chalks on some newspaper.
Let them dry out. Try them on paper. If they are too hard crush them
up add more enamel and enough water to reconstitute the putty-like
texture. If they crumble too easily crush them up and add more water
and few drops of the gum solution reconstitute the putty texture and
roll them out again. You need some texture to draw on. You can
sandblast the glass, etch it or fire on some of Reusche's satin etch
enamel."