Merrifield, Mary P.: The art of fresco painting, as practised by the old Italian and Spanish masters, with a preliminary inquiry into the nature of the colours used in fresco painting: with observations and notes (London: Charles Gilpin, 1846)

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FRESCO PAINTING.

lime, being damp, will yield to the tracing, and receive all the marks.
Then, taking away the cartoon, we must paint upon these with
earthy, but not mineral colours, mixed with clear water; and the
white should be calcined Travertine. This kind of painting
requires great judgment; because, while the wall is wet, the colours
produce a different effect from what they do when it is dry. We
must, above all things, abstain from retouching any thing with
colours containing parchment-glue, yolk of egg, gum, or gum Tra-
gacanth (JDragante), because, then the painting loses its brightness,
and the colours become tarnished, and, in a very short space of time,
turn black. Therefore, whoever paints in fresco, should, each
day, completely finish his day’s work, without having to retouch it
in secco; because thus his pictures will be of longer duration, and he
will be considered a better master. Painting in tempera can be done
upon a dry wall, upon panel, and upon canvass. To paint upon a
dry wall, the wall must be rasped, and two coats of hot glue laid
over it; afterwards the tempera must be made in this manner:—
The yolk of an egg is taken and beaten up well, and a tender fig
branch is ground up in it, and with this material, colours of all kinds
are tempered, because all are good for this kind of painting, except
the white made from lime, which is too caustic (forte); and the
blues, which would turn green with the above mentioned tempera on
account of the yolk of the egg. They must therefore be mixed with
a vehicle of gum or of size from parchment clippings ; this kind of
size may also be used for all the colours, as it is now the custom to
do in Flanders, whence we receive so many beautiful pictures of
landscapes, painted with this vehicle.