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Page 14
(6) _Yellow._--Barium sulphate, 100 parts; lead chromate, 40; finished
lacquer, 40; solvent, 20. This is dried for about 15 minutes at 150�
C.
Almost all pigments other than the above-mentioned are blackened by
contact with lacquer or suspend its drying quality.
Several organic lakes can be used for coloured lacquers, that is to
say, Indian yellow, thioflavin, and auramine lake for a yellow
lacquer; fuchsine, rhodamine, and chloranisidin lake for a red;
diamond sky blue, and patent nileblue lake for a blue; acid green,
diamond green, brilliant milling green, vert-methyl lake, etc., for a
green; methyl violet, acid violet, and magenta lake for a violet;
phloxine lake for a pink. These lakes, however, are decomposed more or
less on heating and fail to give proper colours when dried at a high
temperature.
MODERN METHODS OF JAPANNING AND ENAMELLING WITH NATURAL JAPANESE
LACQUER.
Urushiol, the principal constituent of Japanese lacquer, does not
according to the Japanese investigator, Kisaburo Miryama, dry by
itself at ordinary temperatures, but can be dried with ease at a
temperature above 96� C. In the same way, lacquer that has been
heated to a temperature above 70� C. and has entirely lost its drying
quality can be easily dried at a high temperature. In this method of
japanning the higher the temperature is, the more rapidly does the
drying take place; for instance, a thin layer of urushiol, or lacquer,
hardens within 5 hours at 100� C., within 30 minutes at 150� C., and
within 10 minutes at 180� C. Japanning at a high temperature with
natural lacquer does not require the presence of the enzymic
nitrogenous matter in the lacquer, and gives a transparent coating
which is quite hard and resistant to chemical and mechanical action;
in these respects it is distinguished from that dried at an ordinary
temperature. During the drying, oxygen is absorbed from the atmosphere
and at the same time a partial decomposition takes place.
This method of japanning has its application in lacquering metal work,
glass, porcelain, earthenware, canvas, papier-m�ch�, etc.; because the
drying is affected in a short time, and the coating thus obtained is
much more durable than the same obtained by the ordinary method.
For practical purposes it is better to _thin the lacquer with
turpentine oil or other solvent_ in order to facilitate the lacquering
and lessen the drying time of the lacquer. Since the lacquer-coating
turns brown at a high temperature, lacquers of a light colour should
be dried at 120� to 150� C.; and even those of a deep colour must not
be heated above 180� C. _Most pigments are blackened by lacquer;
therefore the varieties of coloured lacquers are very limited._
FOOTNOTES:
[1] A question has been raised concerning the safety of
Perkins' apparatus, not merely as relates to the danger of explosion,
but also respecting that of high temperature; and it has been asserted
that the water may be so highly heated in the tubes as to endanger the
charring and even inflammation of paper, wood, and other substances in
their contact or vicinity: such no doubt might be the case in an
apparatus expressly intended for such purposes, but in the apparatus
as constructed by Perkins, with adequate dampers and safety valves,
and used with common care, no such result can ensue. Paper bound round
an iron tube is not affected till the temperature exceeds 400�; from
420� to 444� it becomes brown or slightly singed; sulphur does not
inflame below 540�.
SECTION V.
COLOURS FOR POLISHED BRASS--MISCELLANEOUS.
PAINTING ON ZINC OR ON GALVANIZED IRON.
Painting on zinc or galvanized iron is facilitated by employing a
mordant of 1 quart of chloride of copper, 1 of nitrate of copper, and
1 of sal-ammoniac, dissolved in 64 parts of water. To thin mixture add
1 part of commercial hydrochloric acid. This is brushed over the zinc,
and dries a dull-grey colour in from twelve to twenty-four hours,
paint adhering perfectly to the surface thus formed.
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