=Thin Films=, dried at too high a temperature, even without exposure to light, present a brown appearance, their sensitiveness is impaired, and they take too much ink over their entire surface. 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.