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

140 ENAMELS AND ENAMELLING.
be used, but for slower working a weaker pickle is employed.
As a rule the ware should not remain longer than twenty-four
hours in pickle.
When the pickling liquor has been for a long time in use
and has taken up a relatively large amount of iron into
solution, the result of leaving the goods too long in the bath
is that the liquor forms, in presence of the iron, certain in-
soluble basic salts which adhere firmly, as a soft powder,
to the metal and defeat the object of the process. Such
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over-pickled and pickled afresh.
goods must be scoured again with sharp sand
The pickling vats are generally made of hard wood, but
as they are soon corroded and spoiled by the acid it becomes
advisible to varnish them over inside and thereby protect the
wood from contact with the acid liquor.
The higher the temperature of the pickle the more rapid
its action ; consequently the water used is generally warmed
to 30 to 40 C., and the pickling room is kept warm to
prevent the temperature of the liquor from falling. The
scouring room for cleaning the pickled
ware should be
situated next the pickling room and should contain a rinsing
vessel and a boiler, so as to provide a constant supply of hot
water.
When sufficiently pickled, the utensils are taken out of the
bath, rinsed in cold water and turned over to the scourer, who
scrubs them over with fine sharp sand (preferably quartz
sand) until the surface to be enamelled is perfectly bright. In
large works, simple mechanical appliances which perform the
bulk of the work of scouring, in a very short time, may be
advantageously resorted to, the final stages being always done
by hand labour. The next step is to rinse the goods, in order
to remove every particle of adherent sand, after which they
are dried in a special manner, namely, by dipping them in
hot water for a few seconds and then exposing them to the