Historical Painting Techniques, Materials, and Studio Practice

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Why have some green paint layers of verdigris and copper resinate turned

brown while others remained intact? After a search through the treatises fo r

instructions on how to use this dangerous green pigment and a comparison

of the written instructions with the actual methods of applying the pigment

on the paintings, results seemed to suggest that three interesting factors de­

termine appearance: (1) verdigris has to be thoroughly embedded in oil or

an oil-resin varnish to be protected from air and humidity; (2) colored un­

derlayers contribute to the beauty of the green glaze; and (3) admixtures of

yellow lakes or yellow glazes on top of the transparent green layer were

applied to soften the sharpness of the bluish-green tone of verdigris and

copper resinate.

The instructions fo r the use of verdigris emphasize that it should be thor­

oughly incorporated into the medium and covered with varnish as soon as

possible. The early use of verdigris fo r pictura transludda on gold leaf and tinfoil

described by Theophilus, Cennini, and in the Tegernsee Manuscript (ca.

1500) points to this fact (9, 10, 11). The Strasburg Manuscript simply states

that all colors should be ground in oil. It proceeds to explain how to mix

colors and how to achieve good results by painting in several layers, the

painting technique generally fo und in fifteenth-century paintings (12).

In On the true precepts if the art of painting (1587), Armenini gives very detailed

instructions on painting technique, particularly on how to paint green drapery

(13):

if the drape is to be green, one does as follows: After the sketch is made

using somewhat coarse green, black and white, it is lightly painted with a

mixture if verdigris, a little common varnish, and some giallo santo. With

a coarse brush of miniver, one veils the sketch uniformly; next one pats it

either with the palm if the hand or with a little wad if cotton wool covered

with linen, unta the given colour is uniform and no brush strokes can be

detected. And if the result is not to one's satisfaction, after the veiling is

dry one repaints with the same mixture and then pats in the prescribed

way.

He also explains that before veiling, the thoroughly dried sketch has to be

oiled out very thinly to stop the glaze from being repelled by the underlayer.

A painting by Palmezzano depicting the Mystic Marriage if Saint Catherine,

signed and dated 1537, shows exactly this technique in the green drapery of

the throne and St. Catherine's green garment (Plate 9). The pattern of the

textile used fo r dabbing on the glaze is clearly visible (Plate 10). The build­

up shown in the cross section also corresponds to Armenini's instructions

(Plate 11); even the oiling-out layer is visible in ultraviolet light (Plate 12).

The glaze was apparently too viscous to be spread out evenly with a brush,

therefore the glaze was spread by dabbing it with a rag. Traces of textile

pattern are also visible in a Flemish altarpiece, painted in Antwerp around

1520, now at Oxburgh Hall in Norfolk. In the process of dabbing on the

green glaze the artist could not always keep within the outline of his green

drapery, so he had to retouch the background in some places. Minor overlaps

were simply left; one can see the weave pattern of the rag, the glaze is partly

discolored and some green particles are still visible.

Experimentation

As an experiment, some neutral recrystallized verdigris was ground in linseed

oil and the mixture was heated very gently to approximately 50 °C, until the

copper acetate had dissolved and the pigment grain had disappeared. The

mixture was intensely green and quite viscous. It could be spread with a

brush while warm, but congealed very quickly, making the brush strokes very

coarse and imprecise. However, it was quite easy to spread the glaze by dab­

bing it on with a piece of canvas. After a few hours, the glaze dried. Within

a few days the thick brush strokes of green glaze showed drying wrinkles,

whereas the dabbed area looked the same as when it was applied, demon-

Historical Painting Techniques, Materials, and Studio Practice