Enamels and enamelling; an introduction to the preparation and ...

164 ENAMELS AND ENAMELLING.
thickness, that the enamel exhibits the greatest tendency to
chip off.
To improve the appearance and durability of the ware it is
generally enamelled outside as well as in, but with less refrac-
tory masses, and coloured either blue (with cobalt) or brownish
red (with ferric aluminate). For the reasons already given, the
outside coating should be as thin as possible, though naturally
care is bestowed on the finish of the inside.
greater
By following the instructions already given, any manufacturer
will be able, after a little experimenting, to produce
uniform and durable enamelled sheet-iron ware and,
highly ;
given a little experience, it is not difficult to enamel very large
utensils properly, since the sheet-iron goods are much easier
to handle in the muffle than the heaver cast ones.
Latterly, boiler tubes of riveted steel plate have been
enamelled, and specimens of such tubes exhibiting the most
satisfactory qualities are in existence. Of course the production
of this class of goods necessitates the laying down of
special plant for firing the enamels, and the muffles have to be
correspondingly long. As particular skill on the part of the
workmen employed in the firing is requisite, the production of
these tubes forms a special branch of the enamel industry.