CMC helps to bind the glaze and adhere the glaze to the pot.
Sodium carboxymethylcellulose – an organic gum that helps to harden raw glazes and stains, especially those that have little or no clay content. A side effect is that the gum slows down drying of the glaze – this might be an advantage when brushing glazes, but is a disadvantage when dipping or pouring.
In some sources (i.e. Hamer) it is called S.C.M.C. Veegum CER is a 1:1 mixture of CMC and Veegum T.
Chappell gives these instructions for use: Mix 25 g CMC, 1 quart H2O, and 3-5 drops formaldehyde (to prevent decomposition). Let sit several days. Then, shake or stir. Use about 1 teaspoon per 100 g glaze. Gum tragacanth can be substituted but is more expensive.
(courtesy of glazy.org)
Responses