Read Ebook: Photo-engraving Photo-etching and Photo-lithography in Line and Half-tone Also Collotype and Heliotype by Wilkinson W T Wilson Edward L Edward Livingston Editor

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INTRODUCTION.

The improvements made within the last twenty years in the art of printing books have not, until recently, been kept pace with by the methods of illustration. Wood engraving, except for high class and expensive editions, was crude, whilst the use of engravings from copper or steel, or of lithographs, was also restricted to short and expensive editions.

The introduction of the zinc-etching process, in which the picture is first drawn in line, or stipple, or chalk, upon lithographic transfer paper, then transferred to a plate of zinc and subjected to a process of etching in various baths of acid water, marks a new era, replete with great improvements in cheapness, facility of production, and artistic results.

This new process had scarcely been in good working order before it was seen that great improvements might be made by enlisting photography in its service; because in its original form it was necessary that the design be made of the same size as the finished block, which, in many cases, added too much to the expense. But by introducing photography, the size of the original was of no moment; the lens could easily reduce that, and at the same time preserve the proportions, as well as fine down any crudity in the drawing.

The first methods of producing a photo-transfer, were by making a negative from the original, then paper coated with bichromated gelatine was exposed under this negative, and the sensitive gelatine, corresponding with the transparent portions of the negative , being exposed to the action of light was made non-absorbent of water, whilst the sensitive gelatine representing the white portion of the original being protected from the action of light by the dark portion of the negative, still retained its affinity for water. The consequence was that when a roller charged with fatty ink was applied to the wet print, the exposed portions of the gelatine took the ink, but the white portion being charged with water rejected it, the result being a replica of the original in a fatty ink. This was used as an ordinary lithographic transfer and could be transferred to zinc and etched in relief. |xvi|

Such a process was not perfect, and was not suitable for subjects which necessarily should be to scale. So the next improvement was to place a plain mirror between the lens and sensitive plate, so producing a negative in its proper position as regards right and left; then from this reversed negative a print in fatty ink could be made direct on the zinc.

These transfers on paper, or direct prints on the zinc, are restricted entirely to what are generally termed "subjects in line," such as architectural drawings, plans, woodcuts, engravings from steel or copper plates, or lithographs in pure line, in chalk, or in stipple. The attainment of effect of half tones by graduated works of color, thinner or thicker, or the smooth, delicate gradations of a photograph, are not permissible in relief blocks of this kind, although for short numbers this class of subject could be utilized by employing the collotype, heliotype, or lichtdruck methods, which render the half-tones without breaking up of the gradations.

The next step was to perfect the various methods of mechanically breaking up the half-tones of a photograph, and so giving a means whereby a photograph in all its delicacy may be used to illustrate a letter-press article.

Of course, during the progress of rendering photography applicable for relief blocks, its usefulness for intaglio printing was not neglected. And now having entered into very close competition with wood engraving and by modification of the collotype methods, with lithography, photography can now be used for the production of intaglio plates, in half-tones as well as in line.

W. T. WILKINSON.

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PHOTO-ENGRAVING, ETCHING, AND LITHOGRAPHY.

PHOTO-ENGRAVING IN LINE.

APPLIANCES FOR MAKING PHOTOGRAPHIC NEGATIVES.

For all methods of heliographic printing a suitable photographic negative is absolutely necessary, and to produce that negative good apparatus and pure chemicals, used with skill and intelligence, are indispensable.

The studio must be well lighted, with a perfectly firm floor. The dark-room should be kept for negative work only . There must be a roomy sink in front of a good-sized window covered with a non-actinic medium , such as two thicknesses of golden fabric, so as to have plenty of light to see the progress of development by.

The copying camera must have a long bellows and should not be less than 12 by 10, fitted with rack-work, so as to be able to get absolute sharpness in focussing.

The dark slide must be light-tight, and made strong rather than for portability.

The lens should be rectilinear, and should be capable of covering the largest size plate the camera will take quite sharp to the corners. For a 12 by 10 plate a lens with an equivalent focus of about 18 inches will be best.

To the lens must be fitted a reversing mirror of silvered glass, mounted behind the lens by preference, as such a style of mounting not only protects the surface of the mirror from the air, but keeps extraneous light from affecting the brilliancy of the image.

The camera must be mounted upon a solid table fixed upon small grooved or flanged wheels, such wheels running either upon rails fixed upon or in grooves cut into the floor, at right angles to the wall against which the copying board is fitted.

The copying easel is placed perpendicularly in front of, and perfectly parallel with, the camera. As a mirror is used, the camera is sideways to the object, not facing it, as in copying direct.

The easel should be so contrived that it can be raised or lowered, and moved right and left, which double motion is managed by having the easel double; the up and down motion should be obtained by hanging the back portion like a window sash, the weights being exactly the weight of the whole easel, and the pulleys over which the cords go, not running too freely.

At the top and bottom of the back portions of the easel are projecting strips with a rabbet deep enough to allow the front or copying board to slide sideways, but not loosely; this front board should be painted a dead black with white lines in the centre from top to bottom and from side to side, said lines being divided into inches and half inches, from the centre, so that the drawing may be pinned in the exact centre without trouble.

A convenient size for a copying board is 4 feet high by 5 feet wide.

In connection with the camera, the only thing left to describe is the focussing cloth, which should be quite opaque, and of ample size to exclude all extraneous light from behind when focussing.

For focussing the image absolutely sharp, a magnifying glass may be required.

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THE WET COLLODION PROCESS.

THE COLLODION.

Cut the celloidin into thin strips, or, if it be hard, break it up in a clean mortar, and dissolve in the above mixture of alcohol and ether. When dissolved, this forms the collodion.

THE IODIZER

is composed of:

Bromide of Zinc 150 grains. Iodide of Zinc 350 grains. Alcohol 10 ounces.

When the salts are dissolved, filter and add to the collodion.

The filtering is best done by placing a pledget of cotton-wool in the neck of a glass funnel and passing the iodizer through it. To prevent evaporation, lay a glass plate over the funnel.

The iodizer being added to the collodion, shake them up thoroughly and allow to stand for a week to settle, then decant into convenient bottles; this collodion is ready for use in a week, but will improve with age up to six months, after which time it should be mixed with new.

When coating plates with collodion, it is not a wise plan to pour the surplus from the plate back into the bottle from which it was poured. Pour it into another, kept handy for the purpose, the contents of which, at the end of the day's work, empty into the stock bottle after such a quantity as is sufficient for next day's consumption has been decanted into the pourer.

The best bottle from which to pour the collodion upon the plate is the tall capped bottle sold by the dealers as collodion pourers. |12|

THE NITRATE OF SILVER BATH .

The silver bath is a most important factor in the production of good negatives. It must be compounded with care and used with skill.

To make it, dissolve 6 ounces of nitrate of silver in 10 ounces of water, then add 10 drops of collodion, and shake up well; then add 70 ounces of water, and let it stand all night; then filter through a pledget of cotton-wool packed loosely in the neck of a glass funnel, into a clean bottle or jug; then add 1 drachm of nitric acid and let stand all night before trying. Such bottle or jug, and also the glass funnel, must be kept solely for use with the silver bath.

The bath holder may be an upright vessel of the ordinary pattern, with a dipper with which to lower the plate into the solution; or it may be a flat dish with a cover to keep out light and dust, using a silver hook to lift the plate from the solution; if the former shape be chosen, let the dipper be of glass, porcelain, silver wire, or of wood soaked in melted paraffine, but on no account of ebonite, as such a dipper will cause spots, and derange the bath sooner or later.

If a flat dish be used, the best form is of wood lined with asphaltum, hanging on a cradle, the lower end being a well to hold the solution; in this form of bath the plate, after sensitizing, is drained thoroughly before taking it out. This is a great convenience, as not only is silver solution saved, but the dark slide will last much longer.

The bath solution made up as above will be the right strength for work, but as every plate sensitized therein, takes away its modicum of silver, after a certain time it must be strengthened, as it is essential for the production of good work that the solution be kept at a proper strength. The best way of doing this is to add a drachm or two of saturated solution of nitrate of silver, after each day's work has been done, and if the solution be worked in a flat bath, it will be as well to pour it into a jug and filter it before using again; with an upright holder, this filtering will only require to be done about once or twice a week, as any particles of dust, etc., subside and have not the same chance of falling upon the film as in a flat bath; but the addition of the silver solution should be made, and the solution well stirred up with the dipper.

In course of time a silver bath will become contaminated with organic matter from various causes, and can also be supersaturated with ether and alcohol--with iodo-bromo or nitrate of zinc, and will either refuse to work, or only |13| yield imperfect films and thin images. In such cases the best plan will be to take 20 ounces of the solution, dilute it with clean water 60 ounces, filter, and add 6 ounces of nitrate of silver, and again filter, when a new bath will be the result.

The silver in the rejected portion of the old bath should be precipitated as a chloride, by the addition of a solution of common salt, the precipitate dried and sent to a refiner, together with the ashes of the filtering papers and blotting-paper used to drain the plates upon, or to wipe the backs of the plates after leaving the bath and before putting them into the dark slide.

The silver solution named above, is suitable for negatives of subjects in line, but for the production of negatives with delicate half tones, such as portraits, landscapes, or of the many subjects which are photographed direct, then it will be necessary to provide another bath solution, made and managed in the same way, but only containing sufficient nitric acid to just redden litmus paper, as a bath gives the finest half-tones when nearly neutral, or only slightly acid. It should be remembered that the deepest shadows are represented by clear glass in the negative, to insure which would be impossible with the silver solution inclining ever so slightly toward alkalinity.

The nitrate of silver bath may be made up with distilled water, if pure--that is, if the water is bona fide distilled and not merely from waste steam; if this cannot be guaranteed, the best plan will be to get a gallon of tap water, dissolve in it one ounce of nitrate of silver, then add saturated solution of bicarbonate of soda, until an alkaline reaction to litmus paper takes place, then place the lot in white glass bottles, and expose to the action of light for three or four days. During that time the solution will, first of all, turn black, and then will gradually become quite clear, the organic matter--which if not removed, would have caused trouble--falling in a black mass to the bottom.

Now filter the purified water and use it for compounding the nitrate of silver bath, but do not use it for any other purpose.

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