Historical Painting Techniques, Materials, and Studio Practice

sively about the varnishes Turner used. He may have varnished later works
only when they were sold.
Megilps compared to oil medium
There are numerous references in artists' manuals and critics' reviews to megilps,
combinations of mastic varnish and drying oil that gelled on mixing,
and could then be mixed into pure oil paint on the palette (10). Megilps
(thixotropic medium modifiers) had excellent handling characteristics both
for impasto and glazing, but a severe tendency to darken, and to cause cracking
whenever varnish was applied. Such materials had been used and criticized
at least since Reynolds' time. Recent studies have shown that megilps
can be made successfully from linseed oil cooked with lead acetate or litharge,
cooled, and later mixed with mastic spirit varnish (11). These megilps subsequently
show different behavior on aging, and Turner's paint is somewhat
closer to lead acetate megilp. Pure megilp samples from the corners of The
Dawn of Christianity certainly contain lead and behave when heated like artificially
aged lead acetate megilps made from nineteenth-century recipes.
Megilped white paint from this painting and the considerably earlier Dolbadern
Castle has rather a different chemical composition from pure drying oil
(12), being more hydrolyzed and less oxidized, as though a drier were present
from the beginning. Documentary evidence indicates that Turner used lead
acetate in copious amounts.
Megilps are two-component materials whose properties vary significantly as
the oil:resin proportion changes from 1:3 to 3:1. Film-forming capability, the
tendency of the megilp to segregate afterwards, its tackiness, and its ability to
absorb more or less dust than oil paint all depend on the exact proportions.
Turner, who worked fast and fu riously, and never even paused to grind his
pigments finely, must have used a variety of fo rmulations and proportions of
megilp, albeit unconsciously. This has led to variations in degree of yellowing
and solubility in Turner's paintings, and made them very sensitive to cleaning.
Megilps, as well as paints with a startling variety of melting and softening
points, have been fo und in numerous samples from Reynolds's later paintings
of the 1780s. Reynolds's The Death if Dido, one of the "fancy pictures"
wherein he is said to have used paint media that he never allowed his pupils
to use, is particularly rich in megilplike layers and has some very striking
surface defects. They arise when a modified oil layer is applied to fairly pure
oil, whereupon microwrinkles form in the previously stable film, and the
surface later exhibits a rough texture with drying cracks cutting in deeply.
Figure 6. Detail if Anna's veil, painted over clouds and sky, from Joshua Reynolds's The Death of
Dido, ca. 1781. Oil on cal1vas, 1473 X 2407. Courtesy of The Royal Collection, Her Majesty the
Queen.
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Historical Painting Techniques, Materials, and Studio Practice