The Dictionary Of Photography

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

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Canvas, Printing on
Canvas, Printing on. See Silk, Printing on. For enlarg-ing on canvas see Enlarging.
Caoutchouc. See India-rubber.
Cap. The cover used at the time of exposure to open and close the lens. It is also a protection against accidental injury. It is well to have a cap for each end of the lens for greater pro-tection of the glasses. To prevent accidental losing or mislaying of the cap, it may be attached to the lens mount by a piece of string.
Caramel. When ordinary cane-sugar is heated to from 4000 to 4200 F., the molecule of sugarloses the elements of
water, and caramel C,aH1809 is formed. It is highly soluble in water, deliquescent, and has a deep orange-brown colour, which is highly nonactinic. It is used in photography in backing plates as a preventive of halation. The preparation of caramel is easy if sugar is heated in a saucepan over a slow fire and with constant stirring, a very little practical experience being sufficient to enable the operator to guard against over-heating and consequent car-bonisation of the sugar.
Carbide of Calcium. See Acetylene.
Carbolic Acid (Ger., Carbolsaure; Fr. Acide Phenique). CcH5HO = 94. Synonyms: Phenic Acid, Phenol, Phenylic Alcohol, Hydrate of Phenyl. A crystalline substance, -which is not a true acid, obtained from coal tar by fractional distillation. It is a powerful antiseptic and preservative, for which purpose it is added to gelatine and certain mountants. Solubility: 1 in 20 of water, mixes in all proportions with alcohol and ether.
Carbon. An elementary body which is met with in many forms ; native as diamond and plumbago, also together with hydrogen in the coal deposits. The various forms of coke, retort scale, charcoal, and lamp black are nearly pure carbon. Carbon in this latter form is the chief or basic pigment used in the methods of printing known as carbon printing, and a curious process has been devised in which carbon itself (or possibly a metallic carbide), in contact with nitrate of silver, appears to be sensitive to light. (See Carbonised Plates.)