walls of forgotten churches. They will soon be lost forever; it is yet
possible to render them imperishable by means of Mosaic copies; and why
is it not done? The French, at Milan, set an example of this, by
copying, in mosaic, the _Last Supper_ of Leonardo da Vinci; but it was
their plan to do much for Milan, and nothing for Rome; and the
invaluable frescos of Michael Angelo, Raphael, Domenichino, and Guido,
were left to perish.

It takes about seven or eight years to finish a mosaic copy of a
painting of the ordinary historical size, two men being constantly
employed. It generally costs from eight to ten thousand crowns, but the
time and expense are of course regulated by the intricacy of the subject
and quantity of work. Raphael's _Transfiguration_, cost about 12,000
crowns, and the labour of nine years, ten men constantly working at it.
The late works, are, however, of very inferior execution.

The slab upon which the mosaic is made, is generally of Travertine, (or
Tiburtine) stones, connected together by iron cramps. Upon the surface
of this a mastic or cementing paste, is gradually spread, as the
progress of the work makes it wanted, which forms the adhesive ground,
or bed, on which the mosaic is laid. This mastic is composed of fine
lime from burnt marble, and finely powdered Travertine stone, mixed to
the consistence of a paste, with strong linseed oil. Into this paste are
stuck the _smalts_, of which the mosaic picture is formed. They are a
mixed species of opaque vitrified glass, partaking of the mixed nature
of stone and glass, and composed of a variety of minerals and materials,
coloured for the most part, with different metallic oxydes. Of these no
less than 1,700 different shades are in use; they are manufactured in
Rome in the form of long, slender rods like wires, of different degrees
of thickness, and are cut into pieces of the requisite sizes, from the