clear, and hard, and will present a very
elegant impression of the coin. It will also resist the effects of
damp air, which occasions all other kinds of glue to soften and bend
if not prepared in this way.

2345. Method of Hardening Objects in Plaster of Paris.

Take two parts of stearine, two parts of Venetian soap, one part of
pearlash, and twenty-four to thirty parts of a solution of caustic
potash. The stearine and soap are cut into slices, mixed with the cold
lye, and boiled for about half an hour, being constantly stirred.
Whenever the mass rises, a little cold lye is added. The pearlash,
previously moistened with a little rain water, is then added, and the
whole boiled for a few minutes. The mass is then stirred until cold,
when it is mixed with so much cold lye that it becomes perfectly
liquid, and runs off the spoon without coagulating and contracting.
Previously to using this composition, it should be kept for several
days well covered. It may be preserved for years.

Before applying it to the objects, they should be well dusted, the
stains scraped away, and then coated, by means of a thick brush, with
the wash, as long as the plaster of Paris absorbs it, and left to dry.
The coating is then dusted with leather, or a soft brush. If the
surface has not become shining, the operation must be repeated.

2346. Modelling.

Modelling in Cork, Gutta Percha, Leather, Paper, Plaster of Paris,
Wax, Wood, &c.--Modelling, in a general sense, signifies the art of
constructing an original pattern, which is to be ultimately carried
out on an enlarged scale, or copied exactly.

2347. Scale of Construction.

When models are constructed to give a miniature representation of any
great work, elevation, or topographical information, they are executed
in detail, with all the original parts in just and due proportions, so
that the work may be conducted or comprehended better; and if the
model is a scientific one, viz., relating to machinery, physical
science, &c., then it requires to be even still more accurate in its
details. In fact, all models should be constructed on a scale, which
should be appended to them, so that a better idea may be obtained of
the proportions and dimensions.

2348. Materials.

The materials used in modelling are plaster of Paris, wax, whiting,
putty, clay, pipeclay; common and factory cinders; sand of various
colours;