(c) Copying Coloured Objects, Oil-Paintings, etc. With all coloured objects there is only one particular kind to use, and that is the colour-sensitive plate. When the object contains much red, then one sensitised for this colour must be used ; if there is much blue or violet, then must also a yellow screen or filter be employed. In fact, it may be taken for granted that with all oil-paintings a yellow screen is advisable, as it prevents the reflections from the cracks and inequalities of the surface. The best light in which to copy oil-paintings is sunlight. In copying oil-paintings the question of lighting is an important one, as the thicknesses of the coats of paint will show with strong light from one particular direction; at the same time, it must be borne in mind that artists frequently desire to see these inequalities or brush marks, whilst for ordinary purposes the brush marks are objectionable. For the correct reproduction of colours it is necessary to use light filters, which will cut off the action of the blue and violet rays, whilst the red and yellow act. (The composition of these screens for this purpose is given under
As regards the difficulty of mounting the object to be copied on a vertical position, this being more especially a trouble when a subject has to be copied from a book, it is often convenient to lay the original on the floor or a horizontal surface and to arrange for the camera to look downwards : a very easy matter to arrange if the necessary distance between object and camera is approxi-mately determined beforehand. The camera can then be clamped to the edge of a table or some other piece of furniture; better still, in the upper angle of a step-ladder, in which case the adjustment as to distance can be made by supporting the book at the required height. Special stands for the camera, when looking downwards, have been designed, and these generally include an adjustable table or stage. (For a new and remarkable method of copying see Playertype, and for the use of the camera in a vertical position see Camera and Camera Stand.)
Copyright. See Registration.
Cotton and Gun Cotton. See Cellulose, Pyroxyline, and Celluloid.
Crawling. A term applied to such shifting of the paper in the printing frame as makes a portion of the print unsharp. If