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]
§ 87. _Vasari’s own Method._
Since the experience of many years has taught me how to work in oil on a
wall, I have recently, in painting the halls, chambers, and other rooms
of Duke Cosimo’s palace,[217] followed the method frequently used by me
in the past for this sort of work; which method is briefly this. Make
the rough cast, over which put the plaster made of lime, pounded brick,
and sand, and leave it to dry thoroughly; that done, make a second
coating of lime, very finely pounded brick, and the scum from iron
works; these three ingredients in equal proportions, bound with white of
egg sufficiently beaten and linseed oil, make a very stiff stucco, such
as cannot be excelled. But take great care not to neglect the plaster
while it is fresh, lest it should crack in many places; indeed it is
necessary, if one wish to keep it good, to be ever about it with the
trowel or spatula or spoon, whichever we choose to call it, until it be
all evenly spread over the surface in the way it has to remain. Then
when this plaster is dry and some priming or composition laid over it,
the figures and scenes can be perfectly carried out, as the works in the
said palace and many others will clearly demonstrate to everyone.