This process, like photo-engraving, has been the subject of many applications to the Patent Office, but the first notable progress was made by Messrs. Bullock, in 1865. They seem to have gone into the subject thoroughly, as the elaborate and practical specifications prove, but although the patentees issued some fine specimens of their work, and advertised the sale of prepared paper, nothing came of it.

Messrs. Bullock’s method comprises the printing from grained stone tile, or a stone upon which has been laid a transfer, from a stipple plate, or a plate engraved in lines or dots—upon sensitive transfer paper in stiff ink.

The sensitive paper, with such imprint upon it, is exposed to light under a negative, the specks of ink forming a medium for breaking up the half-tones.

Suitable grain may be obtained from machine stippled plates, as well as from grained stone.

Half-tone photo-lithography may also be made by making, from a proof pulled from a machine stipple, or a ruled plate, or a grained stone, a wet, collodion negative, which, being stripped from its glass support (by any of the means mentioned in the chapter on stripped films) is placed between the ordinary half-tone negative and the sensitive surface—zinc, coated with bichromated albumen, or with bitumen, or either of the transfer papers treated of in Part IV.—the result will be a grained transfer.

Grained zinc, coated with bichromated albumen, or with bitumen, and exposed under a very thin half-tone negative, will also yield transfers suitable for a good many subjects, but the most successful methods are modifications of the collographic printing processes.

Transfers made by any of the methods mentioned in the following chapters may be transferred to polished zinc, and then etched in relief, as directed in Part I.

The various methods named in the last chapter for breaking up and transferring to stone the delicate half tints of a photograph from nature, are in a great measure rather crude and do not give the fine results yielded by the following modification of the collotype process, nor are they so certain and simple in their working.

The production of ink photos is as follows: A plate of flat copper is grained by means of graining sand and a piece of litho. stone, the sand being put through a fine sieve (about 120 holes to the inch). The copper plate being, first of all, well polished and without scratches, is placed upon a flat board, the graining sand is then sieved over it, and moistened, then with a light, firm motion of the wrist, the whole of the surface is evenly ground. The operation of graining is very difficult to describe, except to say that the stone muller is shuffled all over the plate until the polished surface of the copper is replaced by an even matt. Renew the sand when necessary. Do not try to get through the operation rapidly by taking large circles, else scratches are sure to result.

The copper plate being grained, it is well washed, back and front, so as to free it from all grit, then coated whilst wet with

Shake well, then filter; coat the plate twice and stand it on a rack to drain and dry. When dry swill the plate under the tap and again dry. These plates may be prepared in advance, as they improve by keeping.

Now prepare the following solutions:

Warm the coated copper plates by letting them lie upon the slab of the drying oven. The drying oven is described in the chapter on collotype printing, and for this process the slab should be at about a temperature of 150°F. Now strain the above mixture through muslin into an invalid’s cup with a long spout, and holding the warm copper plate horizontally on the palm of the left hand, proceed to pour over it as much of the gelatine mixture as will well cover it. Do not have a very thick film, else the grain will be too coarse; nor too thin, or there will be no grain at all. Practice will soon enable the operator to apportion the proper quantity to each plate. As a rough estimate, about one fluidounce of the mixture for a plate 12 × 10 will be required.

The plate being coated, it is placed on the slab of the drying oven and left there until dry. That will take from one and a half to two hours. The exact temperature at which to dry these films cannot be arbitrarily stated, as so much will depend upon the picture which is to be printed; therefore, a few experiments will be necessary before settling down to an exact form of working. A good plan that answers admirably is to raise the water in the tank of the drying oven to boiling point before coating the plate, then coat the plate, lay it on the slab, let the water in the tank boil for a few minutes then turn out the gas and let the plate dry.

The plate being dry it is exposed under a good ordinary (reversed) negative until the whole of the details are well out. Time the exposure by means of an actinometer.

After exposure under the negative, remove the plate from the printing frame and in the dark room cover it with litho. transfer ink by means of a leather roller, taking care that the whole of the surface is well coated with the ink. Now place it in clean cold water for three or four hours, then with a soft {146} sponge remove as much of the ink as will come away. This operation will take time, as every care must be had not to scratch the film.

Now rinse the plate under the tap and allow it to dry.

When dry soak it in cold water for half an hour, then place it on the press (an ordinary letter press), and with a sponge and soft cloth remove the superfluous water from the film; then roll up with a leather roller charged with litho. transfer ink as thick as can be worked. When the image is properly inked up pull a transfer upon good Scotch transfer paper.

Perhaps the first two or three pulls will not be satisfactory; therefore, it will be best to pull a few before using the transfer paper, damping and wiping between each pull just in the same way that is done in printing from a lithographic stone.

A good transfer being obtained, it should be given to a lithographer to put it down upon a grained stone, an operation which requires great skill and experience. The student’s interest will be best consulted by not attempting to give a description of how to transfer to a grained stone.

Another formula for a sensitive coating for the copper plate is

Soak the gelatine till soft; then melt, and add one drachm of bichromate of potash in powder; stir until dissolved; add twenty grains of good fresh dextrine and let the mixture cool to about 120°F.; then add one drachm of liquor ammonia and six ounces of alcohol. The subsequent operation of coating, etc., is the same as above.

This is a process for the production of photo-lithography in half-tone, direct from the negative, without the intervention of a collotype plate from which to pull the transfer, and is a distinct step in advance.

This process has been named papyrotint, being a modification of Captain Abney’s improved method of photo-lithography, named papyrotype. It is specially adapted to the reproduction of subjects in half-tone, such as architectural drawings in monochrome, or subjects from nature, and it is inexpensive. Its advantages over other methods of half-tone photo-lithography are, that a transfer can be taken in greasy ink, for transfer to stone or zinc direct from any negative, however large, without the aid of a medium, the grain or reticulation being obtained simply by a chemical change. The transfer paper being in direct contact with the negative, the resulting prints are sharper than by those processes where interposed media are used; whilst the same negative will answer either for a silver print, platinotype, or a transfer for zinc or stone. The advantage of being able to use a non-reversed negative is very great, now that gelatine plates have so largely superseded those made with collodion.

The method of manipulation is as follows: Any good surface paper is floated twice on a bath composed of

Great care should be taken that the solution is not overheated, and that the paper is coated without bubbles. It is then dried in a temperature of 60°F. The paper will take about ten hours to dry, and in this state will keep for years. When required for use, it should be sensitized by floating on, or immersing in, a bath of

This need not be done in a dark-room, as the solution is not sensitive to light.

The paper, after sensitizing, is dried in a temperature of 70°, and in a dark room. When dry, it is exposed under any half-tone negative, in the ordinary printing frame. It is preferable to print in sunlight, and, for negatives of medium density, an exposure of three minutes is required; but the exposure will vary according to the density of the negative. The correct time of exposure can best be judged by looking at the print in the frame. When the image appears on the transfer paper of a dark fawn color, on a yellow ground, the transfer is sufficiently printed. It is put into a bath of cold water for about ten minutes, until the soluble gelatine has taken up its full quantity of water; then taken out, placed upon a flat piece of stone, glass, or zinc plate, and the surface dried with blotting paper.

The action of the light has been to render the parts to which it has penetrated through the negative partly insoluble, and at the same time granulated. A hard transfer ink is now used, composed of

These are melted together in a crucible over a small gas-jet, and to them are added four ounces of chalk printing ink, and the mixture reduced to the consistency of cream with spirits of turpentine. A soft sponge is saturated with this mixture and rubbed gently over the exposed paper (in this stage the nature of the grain can be best seen). An ordinary letter-press roller, charged with a little ink from the inking slab, is then passed over the transfer, causing the ink to adhere firmly to the parts affected by the light, and removing it from the parts unacted upon. It will be found that with practice, rolling slowly and carefully as a letter-press printer would his form, the ink will be removed by the roller according to the action that has taken place by light, leaving the shadows fully charged with ink, and the high lights almost clear, the result being a grained transfer in greasy ink. The transfer is next put into a weak bath of tannin and bichromate of potash for a few minutes, and when taken out the surplus solution should be carefully dried off between clean sheets of blotting paper. The transfer is hung up to dry, and when thoroughly dry, the whole of the still sensitive surface should be exposed to light for about two minutes. A weak solution of oxalic acid should be used for damping the {149} transfer (about 1 in 100), and this should be applied to the back of the transfer with a soft sponge. After it has been damped about four times, it should be carefully put between clean sheets of blotting paper, and the surplus moisture removed. A cold polished stone is then set on the press, and when everything is ready the transfer is placed on the stone and pulled through twice. The stone or scraper is then reversed, and the transfer is again twice pulled through. A moderate pressure and a hard backing sheet should be used, care being taken not to increase the pressure after the first pull through. The transfer is taken from the stone without damping, when it will be found that the ink has left the paper clean. Gum up the stone in the usual way, but, if possible, let the transfer remain a few hours before rolling up. Do not wash it out with turpentine, and use middle varnish to thin down the ink.

It should have been mentioned that varying degrees of fineness of grain can be given to the transfer by adding a little more ferridcyanide of potassium in the sensitizing solution, and drying the transfer paper at a higher temperature, or by heating the paper a little before exposure, or by adding a little hot water to the cold water bath, after the transfer has been fully exposed; the higher the temperature of the water, the coarser the grain will be. The finer grain is best suited to negatives from Nature, when a considerable amount of detail has to be shown.

The coarse grain is best for subjects in monochrome, or large negatives from Nature, of architecture, etc., where the detail is not so small. Even from the finer grain, several hundred copies can be pulled, as many as 1200 having been pulled from a single transfer. It would have produced a great many more if required.