Page:The color printer (1892).djvu/325

 A roller when in the best condition for taking up the ink and freely giving it off again, should be firmly elastic, and should feel tacky when the hand is gently pressed upon its surface; at the same time, if the hand is moved rapidly along its surface, it should feel smooth and polished as if it was not very tacky. A form roller should be nicely adjusted so that it will be evenly pressed by the vibrator, along its full length, without flattening its surface; at the same time it should firmly but evenly press the face of the form without depositing any ink below the actual face of the type, cuts, etc., contained in the form.

Printing ink should always be adapted to the surface upon which it is to be stamped. If the paper is hard and smooth, then the ink should be somewhat stiff; but if it is soft and rough, then the ink shonld be comparatively thin. Black inks require less impression to make them adhere properly to the surface of paper than any of the colors; the reason being that the coloring matter of which the blacks are made, is generally composed of much finer particles than the colored inks; for this reason very fine half-tone and wood engravings can be printed much cleaner and sharper with black than with any colored ink.

Sometimes it will be found that certain heavy-bodied colors, such as vermilion, orange, etc., will cake on the form and rollers; the reason for this is generally because the varnish in the ink is not quite strong enough to hold the coloring matter, which is very heavy. This trouble can often be overcome by adding a little medium varnish to the ink. Boiled linseed oil is one of the best mediums there is for reducing inks, when a little too stiff for printing upon some papers. It will sometimes be found, however, that linseed oil will not answer the purpose; for instance, we have tried to reduce certain inks which had become somewhat hard, and found that the oil merely separated the hard inks into little buttery masses which could not be united nor reduced to an even con-