Desiccation Or Drying The Well-known Additions Of The Acetate Or

sugar of lead, litharge, and sulphate of zinc, either mechanically

ground, or in solution, for light colours; and japanner's gold size, or

oils boiled upon litharge, for lakes; or, in some cases, manganese and

verdigris for dark colours, are resorted to when the pigments or

vehicles are not sufficiently good dryers alone. It would be well if

lead and copper could be banished from the list of siccatives

altogether: assuredly, no artist with any regard for the permanent

texture of his work should employ them except in extreme cases, and in

the smallest possible quantity. The best of pigments may be ruined by

their injudicious use, and obtain a character for fugacity which they in

no way deserve. It requires attention that an excess of dryer renders

oil saponaceous, is inimical to drying, and is otherwise injurious. Some

colours dry badly from not being sufficiently edulcorated or washed.

Sulphate of zinc, as a siccative, is less powerful than acetate of lead,

but is far preferable in a chemical sense. It is supposed erroneously to

set the colours running; which is not positively the case, though it

will not retain those disposed to move, because it wants the property

the acetate of lead possesses, of gelatinizing the mixture of oil and

varnish. These two dryers should not be employed together, since they

counteract and decompose each other, forming two new substances--acetate

of zinc, which is a bad siccative, and sulphate of lead, which is

insoluble and opaque. The inexperienced ought here to be guarded against

the highly improper practice of some artists, who strew their pictures

while wet with acetate of lead, or use that substance in some other

mode, without grinding or solution; which, though it may promote present

drying, will ultimately effloresce on the surface of the work, throw off

the colour in sandy spots, and expose the paintings to peculiar risk

from the damaging influence of impure air.

It is not always that ill drying is to be attributed to the pigments or

vehicles, the states of the weather and atmosphere have great influence

thereon. The direct rays of the sun are powerfully active in rendering

oils and colours siccative, and were probably resorted to before dryers

were--not always wisely--added to oils, particularly in the warm climate

of Italy. The ground may also advance or retard drying, because some

pigments united by mixing or glazing, become either more or less

siccative by their conjunction. Many other accidental circumstances may

likewise affect drying; and among these none is to be more guarded

against by the artist than the presence of soap and alkali, too often

left in the washing of his brushes, and which, besides other bad

results, decompose and are decomposed by acetate of lead and most

siccatives. In such cases desiccation is retarded, streaks and patches

are formed on the painting, and the odium of ill drying falls upon some

unlucky pigment. To free brushes from this disadvantage, they should be

cleansed with linseed oil and turpentine. Dryers should be added to

colours only at the time of using them, because they exercise their

drying property while chemically combining with the oils employed,

during which the latter become thick or fatten. Too much of the

siccative will, as before noticed, often retard drying.

The various affinities of pigments occasion each to have its more or

less appropriate dryer; and it would be a matter of useful experience if

the habits of every colour in this respect were ascertained. It is

probable that siccatives of less power generally than the compounds of

lead and copper might come into use in particular cases, such as the

oxides of manganese, to which umber and the Cappagh browns owe their

drying quality.

To other good attributes of pigments, it would be well if we could in

Described As Cory's Brown Madder Distilled Verdigris Or More Properly Refined Verdigris The Best Is facebooktwittergoogle_plusredditpinterestlinkedinmail