fixing on walls or floor by laying them home on a float of cement. When
the cement sets, the cardboard sticking to the face is washed off, and
the joints of tesseræ flushed over with cement and cleaned off, leaving
all joints filled up level.

There are other processes used for the same end. The technical processes
need not occupy our attention at present. There is one process that may
appeal to you, and that is executing the work _in situ_ by floating on a
limited expanse of cement, and sticking on the tesseræ at once. It has
the advantage of enabling the artist or architect to see the effect of
his efforts under the fixed conditions of light and height.

I shall confine myself to vitreous or glass mosaic, which for
durability, extended scales of primary colors and their numerous
semi-transparent gradations is unequaled by any substance yet used for
wall or floor decoration. I am surprised, having all these fine
qualities, it is not more used by architects. If you require proofs of
its triumphs, go to St. Mark's, of Venice, and stand under its mellow
golden roof. There you will find its domes and vaulted aisles, nave and
transepts entirely overlaid with gold mosaic, into which ground is
worked--in the deepest and richest colors and their gradations that
contemporary manufacturers could produce--subjects selected from the
creation down to the life of Christ, in addition containing a complete
alphabet of early Christian symbolism. The roof surfaces being one
succession of over-arching curves become receptive of innumerable waves
of light and broad unities of soft shadows, giving the whole an
incomparable quality of tone and low juicy color.

Never use your gold but on curved or undulating surfaces. Flat planes of
gold only give the effect of a monotonous metallic yellow, and can never