CHAPTER IV.
PRINTING FROM THE COLLOTYPE PLATE.
Collotype plates are usually printed from, upon a typographic press, but the best press is one with a cylinder, like the lithographic machines. Such presses give a more even pressure, and at the same time will enable more impressions to be made in a given time.
In the chapter on heliotype printing, a description is given for preparing the tympan for printing from the heliotype skin, and that description holds good for collotype plates; but we shall require a slate slab, the full size of the bed of the press, and a little under half an inch in thickness, upon which to fix the collotype plate by means of plaster of Paris.
The press being ready, take the dried plate, and soak it for half an hour in clean cold water. After that wipe it with a clean soft rag, and scrape any gelatine from the back that may have found its way there; spread as evenly as possible some fine plaster of Paris over the slate slab on the bed of the press, then damp with sufficient water to make the plaster the consistency of cream, and lay the damp collotype plate in the centre, and press it well down, working it a little so as to get it level and well bedded in; allow the plaster to form a ridge all round the edges outside the plate, levelling these ridges by running the finger over the moist plaster, so that they do not project above the face of the plate. Now cover the collotype plate with a mixture of
Glycerine 5 ounces. Water 10 ounces. Ox-gall a little.
Allow this fifteen minutes to permeate the film, taking care that it covers the whole of the surface evenly.
Whilst the plate is thus soaking up, get the inking slab clean, and the two rollers ready, viz.: An ordinary lithographic roller, for inking up the heavier portion of the image, and a composition roller for inking the half-tones and clearing the image; then mix the ink to the desired shade by taking some stiff ink from the tin, and mixing to the proper consistency with a little olive oil. The ink must not be made thin, but just sufficiently softened to work up with |172| the palette knife. The ink used must be very finely ground by machinery with a minimum of olive oil. This, in hand grinding, is difficult to do, and the presence of too much varnish in the ink is prejudicial to the production of bright collotype prints.
The ink being mixed, a little is taken up on the point of a palette knife and smeared along the face of the leather roller and then worked vigorously upon the inking slab, until the ink is thoroughly distributed upon both roller and slab. Do not attempt to thin the ink so as to lessen the labor of distributing the ink, as that will only render the collotype print flat and weak. The ink must be stiff and spare. Now remove the soaking fluid with a very soft sponge, and blot off with fine plate paper, then proceed to roll up with the leather roller, until the image just shows nicely on the plate. Do not attempt to get it to take sufficient ink to look black. Next take the composition roller, and a little ink thinned with lard to about half the consistency of that used with the leather roller, and touch it here and there with the palette knife holding this thinner ink, and roll up on another slab until the ink on the slab and roller are quite even; now apply the composition roller to the image inked up by the leather roller, and roll with a light pressure and quick motion. This will complete the inking up of the image. Now take a piece of the mask paper mentioned for heliotype printing, and having cut out a suitable aperture, place it in position upon the plate, then put a piece of paper in position upon the mask; upon this paper fix a large sheet of smooth waste paper, then loose the blanket, lower the tympan, run the bed of the press under the platen, and after adjusting the pressure, pull over the lever, run out the bed, and examine the proof. From that deduce whether the ink is too thin, or too thick, or not enough, or too much. Damp with a sponge dipped in water, then blot off or remove the surface water with a damp soft rag, then ink up again, and repeat until a suitable print is the result.
Some collotype blocks require the ink far thinner than others, therefore it will be the aim of the printer to try various degrees of ink with each plate until the best result is attained. The best prints are got, as a rule, from a roller that seems to have very little ink upon it, but the ink thoroughly well distributed over both slab and roller.
To print from a collotype plate it is necessary that those portions of the film which have not been exposed to the light—and from them in proportion as the gradation of tone progresses to the shadows—must be charged with moisture to enable them to resist the greasy ink; if plain water be used for this it would |173| be troublesome to get sufficient in the film to resist the ink, and at the same time enable the roller to feed the image without slipping. Therefore glycerine is used, mixed with water, and with various hygroscopic substances, to which the term “etching fluids” has been given. This term is a misnomer, and quite out of place, “damping fluids” being the best.
In addition to the damping fluid previously given, a few others are here appended, each having their advantages under certain conditions:
Glycerine alone or with water.
or,
Glycerine 5 ounces. Water 5 ounces. Hyposulphite of Soda 1/2 drachm.
or,
Glycerine 5 ounces. Water 5 ounces. Nitrate of Potash 1 drachm.
or,
Glycerine 5 ounces. Water 5 ounces. Ammonia 10 drops.
or,
Glycerine 5 ounces. Water 5 ounces. Common Salt 30 grains.
or,
Glycerine 5 ounces. Water 5 ounces. Chloride of Lime 1 drachm.
The last one must only be used when it is desired to take away a tint, and if used too often, will be very likely to destroy the image altogether.
During the printing from a collotype block, the number of impressions that may be pulled without redamping, will vary very much with each block. Sometimes as many as eight or ten may be pulled, but the average will not exceed two. As soon as there is a tendency to flatness, take a sponge containing a little of the damping fluid, and go over the film with it, then wipe it off |174| with another sponge, or a piece of damp cloth (soft), then blot it off with a piece of good blotting paper, and ink up again. In fact, as a rule, it is best to damp for each print.
Good printing paper must be used for collotype prints, and for very fine work a fine neat enamel paper will be best. Coarse hand-made papers, however much admired, must soon break up the delicate image.
I will describe another drying oven, the heating arrangement of which is the same as the other, but the superstructure is much smaller. It will require more care during the time the coated plates are drying to keep the temperature down, but it has the advantage of allowing a thermometer being inserted in the lid in such a manner as to allow the temperature of the interior being seen at a glance. Still another advantage is, it takes up much less room. It measures inside 18 inches wide by 32 inches long, and 9 inches deep to the top of the slab. The thickness of the slate slab and of the copper tank should be the same as in the larger oven; the lid at the top should be made solid and have an orifice in the centre through which the thermometer is pushed. The sides of the oven should be covered with one or two thicknesses of good red flannel.
The only thing that calls for particular attention in these ovens is the copper tank, which should (especially the top) be made of good, stout sheet copper, otherwise the water on being heated has a tendency to make the copper bulge, and elevate the slab. By that means the care which should be taken in levelling the slab will be lost, as this elevation will put it all out. Before putting the superstructure in position, the slab must be cemented to the top of the copper tank by means of plaster-of-Paris; this is important, as a much more even heat is thus obtained.
Now, whichever oven is decided upon, it must be erected in a room free from draught, where it can be kept at a temperature of 70° F., as the quality of the collotype plate is much influenced by the temperature of the room in which it is prepared. So, too, is the oven in which it is dried, especially if below 60°, for then it is very difficult to get good results, as the plate chills when taken from the oven, and the film is almost sure to prove rotten during the printing. |175|
In the summer time, if the room gets too hot, the gelatine solution is apt to get frothy, and then dry hard and glossy, instead of with a nice half-mat surface. It is then best to prepare the plates only in the early morning.
The temperature at which to dry the collotype plates will vary according to the subject to be printed upon them, as some subjects will require a finer grain than others. But a few intelligent experiments will soon enable the operator to judge of the temperature required; 75° F. is the lowest, and 120° F. the highest temperature giving good, bright blacks.
One of the great secrets in collotype is to give a double coating to the plate. I find it really a great advantage so to do. I found this out quite by accident. One day, when I went to use some plates, I found that they had not been properly levelled, and that the coating was thin at one end, and thick at the other. This happened to three out of a batch of four, the other one being all right; so, in a fit of laziness, or hurry, or something, I decided on recoating the three, and did so. When I came to print from the three twice coated and the one once coated, I was agreeably surprised at the difference; the pictures on those twice coated were much more vigorous. Since then I have tried the experiment exactly, and always get the same uniformly excellent results. The second coating is applied as soon as the first is dry; but this second coat cannot be applied so well if the plate be held on the hand, therefore a levelling stand should be used, and the gelatine poured on the centre and coated over the surface by means of a glass rod.
The proper quantity of gelatine solution requisite for a plate 16 by 13 inches is 2 ounces for each coat. Note well that all of it is left on the surface of the plate, not some on the table.
When once the coated plates have been placed in the oven, and the lid is closed down, they must not be disturbed until they are dry; this will be in two or three hours, according to the thickness of the coating of gelatine. If removed before they are dry, there is danger of marking the film.
After the second coating of gelatine is dried, the plate will be all the better if kept a few hours before being printed upon, care being taken to store it in the dark, or somewhere free from damp and gas fumes.
By the bye, the oven must be placed in a room illuminated by yellow light—_i. e._, daylight filtered through yellow glass, cloth, or paper; or else the room must be lighted by gas or oil light.
The negative to be printed from should have all the parts that are intended |176| to be quite white in the finished print, stopped out with India ink or Gihon’s opaque, and the limit of the picture should be masked by very thin tinfoil, cut quite straight and gummed upon the film side of the negative. The rest of the margin of the plate must be protected by a brown paper mask.
The best printing frames for collotype printing are of the box (or “deep”) pattern, with plate glass fronts. They should be about two inches deep, and the bars behind quite plain—_i. e._, without either screws or springs. The back board should also be dispensed with, the pressure being got by means of wedges. The advantage of these frames is that the picture can be examined without undoing the back, and without risk of shifting the plates.
After printing, the plate should be placed in a zinc vessel like a plate box fitted with a siphon, so that the water can be kept constantly changed, until the bichromate is removed; then the plate is drained, and, after being wiped with a soft cloth, is put away to dry.
Now then, beginners, do not be in a hurry to try your first plate on the press directly it is free from the bichromate, as no plate will give a good result until it has been dried down. Before putting it on the press, soak it for half an hour in water, then half an hour in glycerine and water in equal parts, and, finally, wipe it, and proceed to ink up the press.
The safest plan is the one mentioned, viz., bedding up slate with plaster-of-Paris. Another plan is to place on the iron bed of the press a piece of thin felt, then a slab of glass, upon which are placed two thicknesses of wet blotting-paper; upon these place the collotype plate (the back of which is free from any gelatine that may have run over after coating); then, if a chase be placed on the press, the plate may be blocked in position by means of a few pieces of furniture tightened by means of quoins.
In the above only glass slabs are treated of; but brass plates, about one-eighth of an inch thick, will be found safer, and more economical than glass, and yield results just as good. They may be fixed upon a block of hard wood by means of a screw (countersunk) at each corner. If an ordinary type press is not at hand, brass plates may be printed from upon a litho. press.
Whether the plate will require damping each time will depend greatly upon each individual plate and the subject. With some, damping must be done each time; with others, once only for four, six, up to a dozen pulls; but, of course, the temperature of the room in which the printing is conducted will be an important factor in determining this point. When the print is flat, and the whites degraded, then damp the plate before again inking up. |177|
To insure even prints, care must be taken to keep the roller well charged with ink. Much more could be written on this subject, but practice will be the best guide.
A word as to bedding the glass slab on. With a properly prepared leather litho. roller, charged with ink mixed with a little olive oil and varnish, brought to a working consistency with a muller on a smooth slab (be sure that the ink on the roller is evenly distributed), after wiping the plate carefully with a soft, damp cloth, proceed to ink up the image slowly and carefully; then, when all the ink possible has adhered to the image, take the glue roller and apply it three or four times, which will clear the image wonderfully. Now put the mask in position—either a cut-out, or four narrow strips of bank-post coated with gold size and oil, and then dried—then put a piece of mat enamel paper in position, then a piece of common printing paper on top, then a piece of blanket; lower the tympan, run in the bed, and press, and, if the pressure is not too much, the prints will be just as good; but, if too much pressure be used, the paper will be creased and spoiled, and the collotype image is in danger of being cut.
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