Liquid Asphaltum &c Is A Sort Of Mineral Pitch Or Tar Which Rising





liquid to the surface of the Lacus Asphaltites or Asphaltic Lake (the

Dead Sea) concretes there by the natural action of the atmosphere and

sun, and, floating in masses to the shores, is gathered by the Arabs.

The French give it an additional name from the region of the lake, to

wit, Bitumen of Judea; and with the English, from the same cause, it has

the alias of Jew's pitch. Asphaltum is not so called, however, after

the lake, as is asserted by a writer in the Encyclopaedia: it is just the

reverse--Pliny says, "The Asphaltic lake produces nothing but bitumen

(in Greek, asphaltos); and hence its name."



A substance resembling asphalt is found at Neufchatel in Switzerland,

and in other parts of Europe. A specimen of the native bitumen, brought

from Persia, and of which the author made trial, had a powerful scent of

garlic when rubbed. In the fire it softened without flowing, and burnt

with a lambent flame; did not dissolve by heat in turpentine, but ground

easily as a pigment in pale drying oil, affording a fine deep

transparent brown colour, resembling that of commercial asphaltum; dried

firmly almost as soon as the drying-oil alone, and worked admirably both

in water and oil. Asphaltum may be used as a permanent brown in water,

for which purpose the native is superior to the artificial. The former,

however, is now seldom to be met with, the varieties employed on the

palette being the residua of various resinous and bituminous matters,

distilled for the sake of their essential oils. These residua are all

black and glossy like common pitch, which differs from them only in

having been less acted upon by fire, and thence in being softer. At

present asphaltum is prepared in excessive abundance as a product of the

distillation of coal at the gas manufactories, and is chiefly confined

to oil-painting, being first dissolved in turpentine, which fits it for

glazing and shading. Its fine brown colour and perfect transparency are

lures to its free use with many artists, notwithstanding the certain

destruction that awaits the work on which it is much employed, owing to

its tendency to contract and crack by changes of temperature and the

atmosphere; but for which, and a slight liability to blacken, it would

be a most beautiful, durable, and eligible pigment. The solution of

asphaltum in turpentine, united with drying oil by heat, or the bitumen

torrefied and ground in linseed or drying-oil, acquires a firmer

texture, but becomes less transparent and dries with difficulty. If

common asphaltum, as usually prepared with turpentine, be used with some

addition of Vandyke brown, umber, or Cappah brown ground in drying oil,

it will gain body and solidity which will render it much less disposed

to crack. Nevertheless, asphaltum is to be regarded in practice rather

as a dark varnish than as a solid pigment, and all the faults of a bad

varnish are to be guarded against in employing it.





Likewise Known As Spruce Ochre And Ocre De Rue Or More Correctly Liquid Indian Ink Is A Solution For Architects Surveyors &c facebooktwittergoogle_plusredditpinterestlinkedinmail

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