Spots are generally caused by solid particles of grit or other impurities being allowed to find their way into the water in the process of development, or, as in the case of certain peculiar circular spots that often deface the carbon print, such spots are caused by small fragments of tissue broken from the edges in cutting, which, being of the same colour as the prepared surface of the tissue and exceedingly small, often escape notice. They adhere most tenaciously to the surface of the tissue, and if not removed before the print is mounted upon its temporary or final support, cause the mischief referred to; being confined between two surfaces they cannot escape, but are dissolved by the water used in developing the print, swell and make a circular patch, often greatly injuring the picture.
Spots of a different character are produced in quite an opposite direction. Instead of being black they are light, in groups each spot having a dark rim on the outside. They generally occur in under-exposed prints, and are formed by fine particles of air imprisoned between the coating of gelatine and the paper support.
When the tissue is mounted for development and placed in warm water, the fine particles of air swell, and not being able to escape from between the surfaces, impress themselves into the yielding portions of the printed tissue and make the marks above referred to, unless the printing has been deep enough to allow of their removal before development is completed.
CAUSE OF FAILURES IN THE SECOND TRANSFER.
Other causes of failure refer particularly to prints by double transfer, either to paper, opal, ivory, canvas or wood panel or any similar surfaces.
Such failures are generally produced by _soap_, _fat_, or _any kind_ of greasy substances being permitted to find their way into the water in which such prints have been manipulated previous to their final transfer. Another point should be mentioned: the sooner a print intended for second transfer is finished the better the result will be.
PRESSURE MARKS.
Pressure marks are caused by using damp tissue or damp pads in the pressure frame. It is recommended that a piece of waterproof material, such as mackintosh cloth, be placed between the tissue and the padding, and that the pads be as smooth and free from grain as possible. It will be found on close examination that the mottled, spotty appearance, known as pressure marks, closely resemble the texture of the pads behind the tissue.
_Thos. S. Skelton._