Chapter VIII (Xxii.)
Of Painting in Oil on a Wall which is dry.
§ 86 Mural Painting in Oil
When artists wish to work in oil on the dry wall two methods may be followed: first, if the wall have been whitened, either ‘a fresco’ or otherwise, it must be scraped; or if it be left smooth without whitening but only plastered there must be given to it two or three coats of boiled oil, the process being repeated till the wall cannot drink in more, and when dry it is covered over with the composition or priming spoken of in the last chapter. When this is finished and dry, the artist can trace or draw on it and can finish such work in the same manner as he treats the panel, always having a little varnish mixed with the colours, because if he does this he need not varnish it afterwards. The other method is for the artist to make, either with stucco of marble dust or finely pounded brick, a rough cast that must be smoothed, and to score it with the edge of a trowel, in order that the wall may be left seamed. Afterwards he puts on a coat of linseed oil, and then mixes in a bowl some Greek pitch and resin (mastice) and thick varnish, and when this is boiled it is thrown on to the wall with a big brush, and then spread all over with a builder’s trowel that has been heated in the fire. This mixture fills up the scores in the rough cast and makes a very smooth skin over the wall, when dry it is covered with priming, or a composition worked in the manner usually adopted for oil, as we have already explained.216