The author once came upon a garden wall which was decorated with mosaics made from pebbles collected over the years. There were fishes, seagulls, wild boar and a series of other animals, an amusing record of the maker's holidays. He was entirely self-taught and had begun to collect the pebbles at random. Having decided on how to use them, he collected them more deliberately.
Each year on his return from holiday he got a plasterer to cut out a space on the old wall surface about 3 x 5 feet in area and fill it in with a fresh, slightly prominent bed of plaster. He then worked from a rough drawing, pressing the stones, which he kept wet in a trough, into the plaster. The excess plaster was removed with a spoon and spatula and the stones wiped with a damp cloth. The plasterer gave a final touching up to the edges.
The stones looked very dull and pale when they dried, but once the plaster was quite dry and set they were brushed very lightly with hot linseed oil mixed with beeswax, taking care not to touch the plaster and mark it. The stones had first been heated with a blow torch so that the wax had time to penetrate the pores before setting. In a few days' time they were polished with a woolen cloth. This work had not, nor was it intended to have, any artistic pretensions; but far and wide the plaster garden dwarfs found the taste of the neighborhood had become too good for them, and they disappeared without a trace.
There are essentially four different mosaic techniques: odd 5tones or broken slabs pressed into thick plaster; builder's mosaic with strings of pebbles laid in horizontal lines; the al most join less industrial mosaic; and classical freehand mosaic. We can deduce the methods of the others from a knowledge of the classical process. When properly done they are all very durable.
Once the theme and the size of the mosaic is decided in relation to the building we start work on a sketch. It can, and, indeed, should, be very small, so that a certain monumental quality arises from enlargement alone. This is a trick that can be used to some extent in all pictorial art. Nothing is so damaging in mural work, particularly in mosaic, as to use the broad and simple effect in a mass of detail.
The sketch should be carried out in poster colors on paper the color of the plaster, without at first taking the texture of the joins into account. When a simple colored sketch is ready we place over it a sheet of tracing paper and divide up the areas of color into squares corresponding to the size of stones which will be used. This need not be done exactly; the aim here is to get an idea of how the design will 109k in mosaic.
To let the idea develop properly it is best to make an intermediate drawing before the full-size cartoon, about a half or third full size, again painted in continuous colored surfaces. In parts, at least, this can be divided up into the tessera squares, using a soft pencil directly on the drawing. If we feel there is no essential correcting to be done we proceed to an exact drawing of the most important outlines on good tracing paper.
This page is to be kept for reference, and no more work is done on it at present. We now take thick drawing paper and color it to match the surrounding plaster, trace on the outermost outline of the mosaic-if it is to stand free on the plaster surface, and wash inside this outline with a neutral gray waterproof color to represent the shadows of the joins. Unless waterproof, it may run when the colors of the design are put on. Onto this we trace all the outlines of the design, a process best done with white chalk.