5. (Wynn.) Red lead, 18 parts; borax (not calcined), 11 parts; flint
glass, 16 parts; as last.
6. (Wynn.) Powdered flints, 10 parts; nitre and white arsenic, of each, 1
part; as last.
_Obs._ The precise qualities of the products of the above processes depend
greatly upon the duration and degree of heat employed. By increasing the
quantity of sand, glass, or flux, the enamel is rendered more fusible, and
the opacity and whiteness is increased by the addition of oxide of tin.
The use of borax should be avoided, or it should be used sparingly, as it
is apt to make the enamel effloresce and lose colour.
=Enamel, Black.= _Prep._ 1. Calcined iron (protoxide), 12 parts; oxide of
cobalt, 1 part; mix, add an equal weight of white flux, and fuse as
before.