Julius Schnauss

Failures in Collotype.

IN THE PREPARATION OF THE PLATES.

AIR bubbles in the albumen substratum. These must either by filtration or by the aid of a piece of paper be carefully removed from the solution before it is applied to the plates. The latter must be well cleaned and dusted, and freed of emery powder if they have been re-ground.

To Prevent Dust or other matter rising from the edge of the plates by capillary attraction while standing, they should be allowed to rest on clean blotting paper, and preferably on one corner only.

Coating Plates.—Great difficulties are experienced by the beginner in coating the plates with the chromated gelatine. He seldom knows beforehand the exact quantity required, or the temperature of the solution. The latter ought to be ascertained, as it is an important factor in the thickness and flow of the coating; with a solution only just warm it is impossible to apply a very thin coating, while the hotter the gelatine the thinner the layer. Considerable dexterity and judgment are necessary to spread an even layer of the requisite thickness, which is a matter most essential to success, but, unfortunately, only to be mastered by actual experience.

Plates are not unfrequently spoiled by inclining them while conveying them to the drying box, as in this way the coating is frequently rendered uneven.

All solutions must be carefully filtered, and the plates freed entirely from dust. The drying box, particularly the lid, must be carefully dusted and cleaned, but not immediately before use.

Other necessary precautions have been pointed out while describing the preparation of the plates. By strictly adhering to the rules laid down it will be found possible, after a certain amount of practice, to avoid the pitfalls here enumerated, while with regard to faults in the plates, there only remain to be mentioned the consequences of drying at too high a temperature.

Thick Films are extremely liable to fly off the glass and damage its surface, if dried at too great a heat. The thicker the film the lower should be the temperature of the drying box.

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.

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.

Paper Adhering to the Gelatine—Those layers which yield the best and most brilliant impressions, showing plenty of contrast, which have been fully printed under a vigorous negative, most often exhibit a disagreeable tendency to adhere to the paper in the high lights. The greater the proportion of isinglass present in the film the more will this fault manifest itself, particularly with an enamel paper. An application of a diluted solution of ox-gall to the film, the use of a thick well-sized or glazed paper, lighter pressure while printing, and less frequent damping will all tend to diminish this evil. Layers of this nature are extremely liable to damage, and the adhesive portions will soon suffer unless the greatest care is exercised.

Ink Remains upon the Plate.—Through too light or uneven pressure it sometimes happens, especially when using a stiff ink, that the latter will, after the impression has been pulled, partially adhere to the darkest portions of the printing surface, particularly on the edges of plates deeply copied. If this fault is not corrected at once, and the printing allowed to proceed, these portions giving a light, faulty impression will gradually increase in size, and the corresponding portions of the Collotype plate gradually darken. When first observed the whole plate must at once be cleaned with turpentine and again rolled up with thinner ink, a greater and perfectly even pressure being applied. Small faults of this nature occurring on the edges of the plate can be corrected after each faulty impression by means of a small piece of sponge moistened with gum water or with a turpentine rag.

Displacement of the Paper under the scraper will create a double impression, and sometimes wrinkles, the latter invariably leading to the destruction of the plate. By adopting the use of the bridge now used in conjunction with most Collotype hand presses, this fault is avoided, as the paper is only in contact with the printing surface immediately under the scraper.