sides with a much thicker mixture. The paper is kept warm by performing
the operation before a hot fire, and a third and even a fourth coating may
be applied until the texture of the paper is seen to merge into
homogeneous translucency. Paper prepared according to this process is
said to come nearer than any other to the highest standard of perfection
in transparent paper. Care must be used in making, as the materials are
highly inflammable.

DIFFERENT KINDS OF ENGRAVING.

"Line" engraving is of the highest order. All engravings are done in
"line"--simply straight lines. Next comes "line" and "stiple." "Stiple"
means dots--small dots like this:--....--.... These small dots are used to
lighten up the high parts of the face or drapery. It is very hard to
engrave a face in lines, simply, and only master engravers have ever
undertaken it. The masters understand and practice both in "line" and
"stiple." Claude Mellan engraved, in 1700, a full head of Christ, with one
unbroken line. This line commenced at the apex of the nose, and wound out
and out like a watch spring. Mezzotint engravings are produced thus:--The
steel or copper is made rough like fine sand paper. To produce soft
effects, this rough surface is scraped off. If you want a high place or
"high light" in your engraving, scrape the surface smooth, then the ink
will not touch it. If you want faint color, scrape off a little. Such
engravings look like lithographs. Etching is adapted to homely and
familiar-sketches. Etching is done thus:--The copper or steel plate is
heated and covered with black varnish. The engraver scratches off this
varnish with sharp needles, working on the surface as he would on paper
with a pencil. Nitric acid is then passed over the plate, and it eats away
at the steel and copper wherever the needle has scraped off the varnish.
When the varnish is removed with spirits of turpentine, the engraving is
seen in sunken lines on the plate.

HOW TO PRESERVE PENCIL SKETCHES.

The pencil drawings of mechanical draughtsmen and engineers may be
rendered ineffaceable by the following process:--Slightly warm a sheet of
ordinary drawing paper, then place it carefully on the surface of a
solution of white resin in alcohol, leaving it there long enough to become
thoroughly moistened. Afterward dry it in a current of warm air. Paper
prepared in this way has a very smooth surface. In order to fix the
drawing, the paper is to be warmed for a few moments.