Victor Bryant on wed 14 aug 96
Samuel Drew wrote:
<...SODA BICARBONATE AS A GLAZE BY ITSELF
OR AS A PRIMARY INGREDIENT IN A GLAZE?
....HIGH PRICE FRITS... SPRAYING ...HiGH SOLUBILITY...>
Well, short of crushing up old bottles for frit , :-)
I can't see how you can obtain a CHEAP frit. But...
Spraying soda carbonates dissolved in water can produce a variety of
interesting toasted to varnished effects, depending on the colour
and type of body, the firing temperature and, of course, the amount
you spray. If you plan to spray heavily, do protect your shelves.
You could stand a pot on a piece of broken kiln shelf painted with
kiln wash or dust with alumina.
Soda compounds are very water-soluble and when you spray, pour or
dip with them, soda readily seeps into a porous body such as a
biscuited pot. It is a strong flux from very low temperatures, so
large amounts soaked into a pot could cause the body to flux more,
with potentially disasterous results such as bloating, warping etc.
HOW ABOUT AN ANCIENT SLUSHY METHOD
Have you considered spraying or brushing a LEATHER HARD pot with
soda ash or bicarb (or even dipping)? There will be much less soda
penetration of the body than on a dry porous bisque pot and funnily
enough some of this links up with the 'egyptian' quartz frit info. I
posted on ClayArt some days ago.
The ancient mesopotamian potters first developed 'proper' glazes by
brushing a slushy version of quartz frit paste onto leather hard pots
- probably with an increased amount of soda ash to improve fluxing.
You could follow their example and brush slushy soda rich glazes
onto leather hard pots.
TRY A MODERN VERSION
Use any low temperature glaze recipe you are familiar with, take out
that expensive frit and replace it with soda ash or sodium
bicarbonate. Mix it with only sufficient water to enable you to
brush it on. Experiment with thick and thin applications. To spray
such glazes you would need to have the other materials ground very
Hope some of this is useful.