Encyclopædia Britannica 1771/II

Encyclopædia Britannica; or, a Dictionary of Arts and Sciences, compiled upon a new plan. In which The different Sciences and Arts are digested into distinct Treatises or Systems; and The various Technical Terms, &c. are explainged as they occur in the order of the Alphabet II, Edinburgh [Andrew Bell – Colin Macfarquhar] 1771.

pp. 632

FRESCO, a method of painting in relievo on walls, so as to endure the weather.

It is performed with water-colours on fresh plaster; or on a wall laid with mortar not yet dry. This sort of painting has a great advantage by its incorporating with the mortar, and, drying along with it, becomes very durable.

The compost should be made of rubbish stones mix with well burnt flint, or lime, and water: but the saltness of the lime must be washed out, by pouring water frequently on it. But this should not be done in moist weather.

To prevent the plaster from peeling, strike into the joints of the wall stumps of horse-nails six inches distant from each other. First plaster the walls pretty thick; then let it dry for some time, the design and colours being first ready prepared. This painting is chiefly performed on walls and vaults newly plastered with lime and sand; and the plaster is only to be put on in proportion as the painting proceeds.

Plaster the wall a second time, about the thickness of half a crown, only so much as you intend to work upon; and while it is wet, work the colours therein, which will incorporate with the plaster so as never to wash out.

The painting must be worked with a free hand, and your colours made high enough at first, as there can be no alteration made after the first painting.

In this work scarce any thing else is used but earths, which still retain their colour, defending it from the burning and salt of the lime. The colours are white, made of lime slacked some time, and white marble dust, red and yellow oker, violet red, verditer, lapis lazuli, smalt, black, Spanish brown, Spanish white, &c. all which are grounded and worked up with water.

The brushes and pencils for this work must be long and soft, or else they will rake and raze the painting: the colours must be full and flowing from the brush, and the design or cartoon must be perfect in the paper-copy.