The ingredients in alkaline glazes are soda-ash, whiting, feldspar, flint and oxide of tin.
Scalded or simmered in a lye of soda-ash of about only 2-3rds the former strength, and washed.
The soda-ash used by the soap-boiler, contains in general about 36 per cent.
It is chiefly obtained as a by-product in the manufacture of soda-ash by the Leblanc process (see Alkali Manufacture).
If the alkali be soda-ash of 40 per cent., half the weight will of course suffice.