The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Asphalt Prooess
Russian or Hungarian turpentine may be made, which oils, when used alone, would attack the image. As restrainer in developing, an addition of ligroin, benzoline (petroleum benzine), or wood oil may be used. The development is best effected by merely rocking in a dish without the help of any pad of cotton wool; and soon, when the image is developed clear, it should be well washed in a stream of water and allowed to drain and dry. (In order to avoid the unpleasant action of adhering drops of water, the plate may be washed with petroleum benzine before wash-ing with water.) It is advantageous before gumming the plate to expose it, as the image adheres better. Valenta also sug-gests the following simplified method of preparing light-sensitive sulphurised asphalt or bitumen: - ioo grammes of raw Syrian asphalt are to be boiled with an equal quantity of commercial pseudo-cymene in which 12 grammes of sulphur flowers have been dissolved. When, after about three or four hours, the formation of sulphuretted hydrogen has ceased, the cymene is distilled off, and the product is the light-sensitive asphalt from which the film is prepared in the usual way by solution in benzol-. The new preparation is soluble in benzol, toluol, cymene, xylol, and turpentine ; it is said to be even more sensitive than that prepared by Valenta's other method. Bitumen is used in several photomechanical processes for making a light-sensitive film, and raw bitumen for laying the ground in photogravure. A kind of artificial asphaltum has been prepared from petroleum, Messrs. Mabery & Byerley having found that, if petroleum is slowly distilled in a current of air, and at a temperature not exceeding 6500 F., asphalts of various degrees of hardness are formed. They do not appear, however, to have studied the sen-sitiveness to light of the new asphalts, but being able in some sense to control these, the viscosity or brittleness of the product should be an advantage in those etching processes on metal in which dusted on resists are used. (See the following article, Asphalt Process.)
Asphalt Process, or Bitumen Process. This process is the first by which a fixed photograph, in the ordinary sense of the term, was produced, and it is still employed in making photo-etched blocks and plates. Niepce, as early as 1827, produced a photo-graph of Kevv Church on a metal plate coated with a bitumen