The work on a mosaic began with the creation of preliminary drawings.
The composition of the mosaic was done in oil on canvas or more often with watercolour on paper. Artists were to follow the palette of shades of stones rather than pictorial principles and chromatic instructions, but maintaining the recognizability of plant or bird species was mandatory. A master had a task to find natural colours of stones which would create a sense of light and shadow, give volume to the image, and recreate the natural pattern of grass or, say, bird feathers.
Each detail was carved from the thinly cut stones with a special tool — archetto, after which the edges were filed to be smooth for a perfect fit with the adjacent elements. The harder a stone is, the easier it is to work with it. Hence the Italian name of the technique — "hard stones". But it was not limited to only hard stones; in each mosaic you can find, for example, several types of marble, which, according to the Mohs scale, are soft stones (It. pietre tenere).
The panels were assembled from the back and then glued to a prepared base — a slate board. When creating tabletops, slate with mosaic was applied to a stone slate (sandstone).
This video shows a step-by-step work on a small decorative panel done in an authentic technique.