Of Lead &c





The heaviest and whitest of these are the best, and in point of colour

and body, are superior to all other whites. When pure and properly

applied in oil and varnish, they are comparatively safe and durable,

drying well without addition; but excess of oil discolours them, and in

water-painting they are changeable even to blackness. Upon all vegetable

lakes, except those of madder, they have a destructive effect; and are

injurious to gamboge, as well as to those almost obsolete pigments, red

and orange leads, king's and patent yellow, massicot, and orpiment. With

ultramarine, however, red and orange vermilions, yellow and orange

chromes, yellow and orange and red cadmiums, aureolin, the ochres,

viridian and other oxides of chromium, Indian red &c., they compound

with little or no injury. Lead colours must not be employed in

water-colour or crayon painting, distemper, or fresco. The whites of

lead are carbonates of that metal, with two exceptions:--Flemish white

or the sulphate, and Pattison's white or the oxychloride. In using all

pigments of which lead is the basis, cleanliness is essential to health.



White lead, by which we must be understood to mean the carbonate, always

contains when commercially prepared a certain proportion of hydrated

oxide. The less of the latter there is present, the better does the

white cover, and the less liable is it to turn brown. The products

formed by precipitation have proved to be inferior in body: otherwise,

pure mono-carbonate of lead-oxide, obtained by mixing solutions of

carbonate of potash and a lead-salt, might be best adapted for a

pigment. However, such a carbonate has been lately produced by Mr.

Spence's process of passing carbonic acid gas into a caustic soda or

potash solution of lead, and for this white an opacity is claimed equal

to that of the ordinary compound.



Great as is the opacity of white lead, it is apt to lose that property

in some measure in course of time, and become more or less transparent.

If, over a series of dry oil-colour rubs of varied hues, there were

brushed sufficient white lead paint to utterly obscure them, after some

years those rubs would indistinctly appear, and by degrees become more

and more visible, until at last their forms--if not their very

colours--could be recognised. From this it would seem that white lead

must slowly but surely part with some of its carbonic acid, and be at

length converted into dicarbonate, a compound possessing less carbonic

acid, and less coating power.



Impure air, or sulphuretted hydrogen, browns or blackens white lead,

converting it partially or wholly into sulphide. It would appear from

the recent investigations of Dr. D. S. Price, that white lead is less

liable to be thus affected, when the pictures in which it is used are

exposed to a strong light; also, that when such pictures have so

suffered, a like exposure will restore them. We have ourselves noticed

the rapidity with which an oil rub of white lead that has been damaged

by foul gas, regains its former whiteness when submitted to air and

sunshine. The action of drying oils has been likewise proved to be very

powerful upon sulphide of lead, an exposure to light for a few days only

being sufficient to change a surface of it, coated with a thin layer of

boiled linseed oil, into a white one. Probably, these agents may have a

similar effect upon other pigments injured by sulphuretted hydrogen, and

many of the colours in paintings may be restored by treating them with

boiled linseed oil, and submitting them to a strong light. That the

result is due to oxidation, there can be no doubt. Indeed, the eminent

French chemist, M. Thenard, was consulted some years back upon the means

of bringing to their original whiteness the black spots which had formed

upon a valuable drawing, by the changing of the white lead, and

employed for that purpose oxygenated water. He had ascertained its power

of converting the black sulphide of lead into the white sulphate, and,

by touching the spots with a brush dipped in the fluid, soon succeeded

in restoring the drawing to its primitive state. Here, again, the use of

the agent might doubtless be extended to other colours, to which foul

air is inimical.



In oil painting white lead is essential in the ground, in dead

colouring, in the formation of tints of all colours, and in scumbling,

either alone or mixed with other pigments. It is also the best local

white, when neutralized with ultramarine or black; and it is the true

representative of light, when warmed with Naples yellow, or orange

vermilion or cadmium, or with a mixture of the yellow and either of the

orange pigments, according to the light.



Ordinary white lead is often mixed with considerable quantities of heavy

spar, gypsum, or chalk. These injure it in body and brightness, dispose

it to dry more slowly, keep its place less firmly, and discolour the oil

with which it is applied, as well as prevent it dissolving completely in

boiling dilute potash-ley, a test by which pure white lead may be known.



The adulteration of pigments, which we have in some instances found

practised to a large extent abroad, is comparatively unfrequent in our

own country, so far at least as regards the superior class of colours

employed by artists. As a rule, such colours when manufactured in

England may be fairly assumed to be genuine; and certainly the

respectable colourmen of the present day are not in the habit of

sophisticating them. We must bear testimony, indeed, to the zeal with

which they purvey, regardless of necessary expense, the choicest and

most perfect materials. This should be a matter of congratulation to the

painter, who must of necessity rely on the faith and honesty of his

colour-dealer; for if he were ever so good a chemist, it would be

impossible for him to analyse each pigment before proceeding to use it.

The fault must rest with himself, therefore, if, through a mistaken

economy, he do not frequent the best houses and pay the best prices. Of

a surety, the colours of the artist are not among those things in which

quality can, or should, be sacrificed to cheapness.



TTITLE BLANC D'ARGENT, OR SILVER WHITE.





Of Late Years In The German Coelin Known Here As Cerulian Blue And Of Shades Between The Extremes Of Light And Dark As Each Compound facebooktwittergoogle_plusredditpinterestlinkedinmail

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