OF SGRAFFITO WORK
The Italian words Graffiato, Sgraffiato, or Sgraffito, mean "Scratched," and scratched work is the oldest form of graphic expression and surface decoration used by man.
The term Sgraffito is, however, specially used to denote decoration scratched or incised upon plaster or potter's clay while still soft, and for beauty of effect depends either solely upon lines thus incised according to design, with the resulting contrast of surfaces, or partly upon such lines and contrast, and partly upon an under-coat of colour revealed by the incisions; while, again, the means at disposal may be increased by varying the colours of the under-coat in accordance with the design.
Of the potter's sgraffito I have no experience, but it is my present purpose briefly and practically to examine the method, special aptitudes, and limitations of polychrome sgraffito as applied to the plasterer's craft.
First, then, as to method. Given the wall intended to be treated: granted the completion of the scheme of decoration, the cartoons having been executed in several colours and the outlines firmly pricked, and further, all things being ready for beginning work. Hack off any existing plaster from the wall: when bare, rake and sweep out the joints thoroughly: when clean, give the wall as much water as it will drink: lay the coarse coat, leaving the face rough in order to make a good key for the next coat: when sufficiently set, fix your cartoon in its destined position with slate nails: pounce through the pricked outlines: remove the cartoon: replace the nails in the register holes: mark in with a brush in white oil paint the spaces for the different colours as shown in the cartoon, and pounced in outline on the coarse coat, placing the letters B, R, Y, etc., as the case may be, in order to show the plasterer where to lay the different colours—Black, Red, Yellow, etc.: give the wall as much water as it will drink: lay the colour coat in accordance with the lettered spaces on the coarse coat, taking care not to displace the register nails, and leaving plenty of key for the final surface coat.
In laying the colour coat, calculate how much of the colour surface it may be advisable to get on the wall, as the same duration of time should be maintained throughout the work between the laying of the colour coat and the following on with the final surface coat—for this reason, if the colour coat sets hard before the final coat is laid, it will not be possible to scrape up the colour to its full strength wherever it may be revealed by incision of the design. When sufficiently set, i.e. in about 24 hours, follow on with the final surface coat, only laying as much as can be cut and cleaned up in a day: when this is sufficiently steady, fix up the cartoon in its registered position: pounce through the pricked outlines: remove the cartoon and cut the design in the surface coat before it sets: then, if your register is correct, you will cut through to different colours according to the design, and in the course of a few days the work should set as hard and homogeneous as stone, and as damp-proof as the nature of things permits.
The three coats above referred to may be gauged as follows:—
Coarse Coat.—2 or 3 of sharp clean sand to 1 of Portland, to be laid about ¾ inch in thickness. This coat is to promote an even suction and to keep back damp.