The best means of producing these effects is by printing from a steel
plate or lithographic stone on thin transfer paper, which, in turn, is
made to give up the design to the surface of the glass, the exposed
portions of the latter being then etched with acid.
In preparing the steel plate, a coating of varnish is prepared by
mixing 200 parts by weight of oil of turpentine, 150 of Syrian
asphaltum, 100 of beeswax, 50 of stearin, and 50 of Venice turpentine
in the warm. The design is then copied in outline by tracing from the
original, the shading being reproduced in a less detailed manner, but
with fewer and bolder strokes, in order to adapt the picture to the
process. It is then pricked through the tracing paper on to the
varnish coating of the plate, and, after clearing out the lines with
graving needles, the plate is etched with a mixture of 1 vol. of water
and 4 to 7 vols. of nitric acid, either by application or immersion;
in the latter event the back of the plate must be varnished over. When
the metal is bitten by the acid to about 1-75 of an inch in depth, the
operation is finished.
To transfer the design to the glass it is printed from the steel plate
on to thin silk paper, the ink used being compounded from 500 parts of
oil of turpentine, 1,500 of Syrian asphalt, 500 of beeswax, 400 of
paraffin, and 300 of thick litho varnish. The printing is performed in
the usual manner, and the transfer laid on the warmed surface of the
glass sheet or ware to be decorated, rubbed over uniformly with a
cloth to make the ink adhere to the glass, and then the paper is
moistened and taken off again, leaving the imprinted design behind. It
is well to have the ink fairly thick, and rely on warmth to impart the
necessary fluidity; otherwise the design may come away with the paper
in patches, and be imperfect.
For etching in the design on the glass, the edges of the latter are
coated with the protective varnish, and then hydrofluoric acid is
brushed over the exposed portions, which are thereby corroded, leaving
the parts covered by the ink standing in relief. According as a clear
or frosted etching is desired, the etching liquid is modified, being,
for the latter purpose, composed of 500 parts of ammonium fluoride,
100 of common salt, 300 of fuming hydrofluoric acid and 30 of ammonia.
This is brushed over the glass two or three times, and then rinsed off
with lukewarm water. For deep etching, hydrofluoric acid is diluted
with 1½ vols. of water and stored for twenty-four hours before use.
The objects are immersed in the baths for thirty to fifty minutes, and
kept quite still the while. If the etching is to be left clear, the
acid is neutralized by boiling the glass in soda, but if to be frosted
afterward it is coated with the first named etching liquid while still
damp. Finally, the ink is washed off with turpentine, the glass rubbed
over with sawdust, washed in hot lye and rinsed with water.
Grained or lined designs can be very suitably printed from a litho
stone, on paper faced with a mixture of 1,500 parts of water, 250 of
wheaten starch, 1,000 of glycerine and 200 of a thick solution of gum
arabic, the ink for printing being prepared by melting and mixing 500
parts of pure tallow, 250 of white beeswax, 250 of liquid mastic, and
150 of pale resin, with 100 parts of lampblack, 5 of minium, and 500
of litho varnish. In transferring the design to the glass, the latter,
if flat, may be passed between India rubber rollers or protected by
layers of gutta percha when the pressure is applied. The impression
produced by this lithographic process has to be strengthened to enable
the thin coating of ink to resist the etching liquid, and this is done
by dusting powdered resin over the printed surface of the glass,
brushing off all that does not adhere, and causing the remainder to
attach itself to the ink by means of warmth, and so form an impervious
covering. The further treatment is the same as that already described.
These methods are particularly suitable for reproducing landscapes,
etc., on thinly flashed glass of various colors.--Diamant.
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