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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.


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