entine. It yet
remains to be seen whether rubber can be synthetically produced
certainly and cheaply. The result of further experiments will be
awaited with interest, as the production of artificial rubber at
moderate cost would be an event of enormous importance.

* * * * *

DEEP AND FROSTED ETCHING ON GLASS.

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 clea