[Illustration: FIG. 5.--Greuzburg's Japanning Oven.]

1. _Stoves heated by direct fire._--These were, of course, the form in
which japanning ovens were constructed somewhat after the style of a
drying kiln. Fig. 5, Greuzburg's japanning oven heated on the outside
by hot gases from furnace. The oven is built into brickwork, and the
hot gases circulate in the flues between the brickwork and the oven,
and its erection and the arrangement of the heating flues are a
bricklayer's job. Coke containing much sulphur is objectionable as a
fuel for enamel stoves Mr. Dickson emphasizes this very forcibly. He
says: "In the days when stoves were heated by coke furnaces, and the
heat distributed by the flues, the principal trouble was the escape of
fumes of sulphur which caused dire disaster to all the enamels by
entering into their composition and preventing their ever drying, not
to speak of hardening. I have known enamels to be in the stoves with
heat to 270° for two and three days, and then be soft. The sulphur
also caused the enamels to crack in a peculiar manner, much like a
crocodile skin, and work so affected could never be made
satisfactory, for here again we come back to the first principle,
that if the foundation be not good, the superstructure can never be
permanent. The enamels, being permeated with sulphur and other
products from the coke, could never be made satisfactory, and the only
way was to clean it all off. The other principal troubles are the
blowing of the work in air bubbles, which is caused mainly by the heat
being too suddenly applied to the articles, but these are very small
matters to the experienced craftsman."

[Illustration: FIG. 6.]