FAILURES IN PRINTING.
It is generally an advantage to work the press in a cool and somewhat damp apartment.
Breakage of the Plate.—Notwithstanding its thickness, the glass plate sometimes flies to pieces on pulling the first impression. If the plate and its foundation are perfectly level the breakage must arise from the presence of some foreign substance having found its way between the two surfaces.
This may occur from such a trivial matter as a grain of sand, perhaps introduced between when moistening the under side of the plate to secure adhesion. Or traces of chromated gelatine may be found attached to the under surface of the plate, either of which causes is quite sufficient to account for a breakage with even moderate pressure. In Collotype the pressure need not be by any means so heavy as in lithographic printing; it should be evenly distributed, and may be moderated by placing the stone or glass plate, or whatever the Collotype plate may be attached to, on some comparatively elastic bedding, which may consist of several layers of printing paper, thin felt, thick indiarubber sheeting, or linoleum, any of which may be used.
Spotted Impressions.—The plate yields unsatisfactory copies covered with white spots resembling drops of water. This most frequently occurs at the commencement of the printing, and is nearly always caused by uneven damping of the surface. Old plates which have been dried very often give perfect negative impressions at first. In such cases, after the removal of the ink by turpentine, soak the plate for a quarter of an hour in water, to which has been added a little glycerine and ammonia (see “Etching Fluid”). Dry the plate with a clean roller covered with cloth or chamois leather—or, as a substitute for the roller, a soft linen cloth may be used—and again roll in with ink which has been thoroughly well distributed on the inking slab.
Too Much Ink is taken by the plate over the whole surface, and notwithstanding slow or rapid rolling, it refuses to leave the high lights. Cause—over-exposure in proportion to the thickness of the layer, which is probably too thin. In such cases washing with dilute solution of ammonia will often improve matters. Another proceeding to be recommended in the case of a plate taking too much ink is to remove all ink by means of a sponge damped in water containing a little petroleum—not benzine or turpentine—and afterwards wash the plate with a sponge containing glycerine and water. It is then ready for immediate printing from, and ought to give about 200 copies without further damping if the press be in a moist situation.
Loss of Half-tone arises from the print layer becoming too moist, when the more delicate half-tones fail to print. Dry with blotting paper, and immerse for five minutes in a bath of alcohol; this will take up the water, and the succeeding impressions will be greatly improved.
Uneven Inking.—It sometimes occurs, particularly in pictures which should show a white ground, that the latter takes more ink in one part than another. This usually arises from an unequal thickness of the sensitive coating. The plate will take most ink where the coating is thinnest, and for this fault there is no remedy.
Ink Refused by the Plate.—Sometimes, after a few impressions have been pulled, the plate refuses to properly take the ink, from the layer being too thick and having been too freely moistened. Further damping should be discontinued and a thinner ink used, which will better take upon the deep-lying shades. This fault will be found most pronounced in the cases of written or printed titles to pictures, and other cases exhibiting extremely disproportionate action of light. Therefore, when there is writing to a picture, it should be shaded somewhat during printing in the printing frame, or if the contrast be very violent it may fail to print entirely.
Flat Prints.—After a number of satisfactory prints have been produced the succeeding ones become flat, this fault will be especially noticeable with thin layers devoid of isinglass, and in cases where the negative has been too flat and lacked contrast. Dampen more frequently with dilute ammonia and glycerine.