Liquid Indian Ink Is A Solution For Architects Surveyors &c





TTITLE IVORY BLACK



is ivory charred to blackness by strong heat in closed vessels.

Differing chiefly through want of care or skill in preparing, when well

made it is the richest and most transparent of all the blacks, a fine

neutral colour perfectly durable and eligible both in water and oil.

When insufficiently burnt, however, it is brown, and dries badly; or if

too much burnt, it becomes cineritious, opaque, and faint in hue. With a

slight tendency to brown in its pale washes, this full, silky black is

serviceable where the sooty density of lamp black would be out of place.

It is occasionally adulterated with bone black, a cheaper and inferior

product.



Being nothing more nor less than animal charcoal, ivory or bone black

had best not be compounded with organic pigments, in water at least. It

is well known that this charcoal possesses the singular property of

completely absorbing the colour of almost any vegetal or animal

solution, and of rendering quite limpid and colourless the water charged

with it. If a solution of indigo in concentrated sulphuric acid be

diluted with water, and animal charcoal added in sufficient quantity,

the solution will soon be deprived of colour. The more perfect the ivory

or bone black, the more powerful is its action likely to be: either over

or under calcined, animal charcoal is less energetic; in the former

case, because it is less porous; in the latter, because the animal

matter, not being wholly consumed, makes a kind of varnish in the

charcoal which interferes with its acting. To a greater or less extent,

gums, oils, and varnishes serve similarly as preventives, thereby

decreasing the danger of employing these blacks in admixture; but, in

the compounding of colours, nothing is gained by needless risk. To mix

with organic pigments, therefore, blue or lamp blacks should be

substituted for those of ivory or bone; that is, vegetal charcoal should

be used instead of animal. It is a question whether even with inorganic

pigments the adoption of the former in admixture would not be advisable.

It was once the general opinion that the action of animal charcoal was

limited to bodies of organic origin, but it has since been found that

inorganic matters are likewise influenced. "Through its agency," says

Graham, "even the iodine is separated from iodide of potassium;" whence

probably pigments containing iodine would suffer by contact. The

investigation of Weppen appears to prove that the action of the charcoal

extends to all metallic salts; with the following, no doubt remains of

this being so, to wit:--the sulphates of copper, zinc, chromium, and

protoxide of iron; the nitrates of lead, nickel, silver, cobalt,

suboxide and oxide of mercury; the protochlorides of tin and mercury;

the acetates of lead and sesquioxide of iron; and the tartrate of

antimony. Whether animal charcoal exercises any deleterious influence on

pigments consisting of these metals, and, if so, how far and under what

circumstances, can only be answered when our knowledge of the properties

of pigments is greater than it now is. At present, perhaps, it is safer

to choose vegetal charcoal for mixed tints, inasmuch as, although it

shares the property of bleaching in a certain degree, it does not

possess the same energy.



TTITLE LAMP BLACK,





Liquid Asphaltum &c Is A Sort Of Mineral Pitch Or Tar Which Rising Liquid Sepia Seppia Or Animal Aethiops Is Named After The Sepia facebooktwittergoogle_plusredditpinterestlinkedinmail

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