James E. Masters

We hope this article will lead many of our readers to try their hands at gum-bichromate.

Gum-bichromate would seem in theory the simplest of printing processes, but in actual practice it will be found to be the most difficult. Prepared according to the method-about to be described, it certainly has the advantage of cheapness. This latter quality is not-one to be generally recommended, but in the case of the beginner in gum printing, who is almost certain to waste plenty of material during his early efforts, anything tending in the direction of economy is worthy of consideration. If the reader decides to prepare his own paper, his total outlay for the necessary equipment need not be more than sixpence. The materials required will be a brush for coating - a one inch flat hog hair brush will answer perfectly; an ounce of potassium bichromate, an ounce of gum arabic, and a sheet of cartridge paper.

The bicromate should be made up in a saturated solution, and the ounce of gum dissolved in 2 1/2 ounces of water and then strained through fine muslin, in order to remove all impurities. The paper to be coated should be a little larger all round than the actual size required, and it will be found that the penny sheet of paper will be cut into nine pieces, each allowing ample margin for whole plate size.

Before coating, it will be well to place an old negative on the paper and run round the edges with lead pencil. This will ensure the requsite surface being covered, and will also be a guide as to whether the coating has been done properly.

The best pigment to start with is lamp-black, and instead of wasting money buying this, the writer scrapes a little as required from the inside of his dark room lantern. To coat the paper, mix equal portions (say $ ounce) of the bichromate and gum solution in a measuring glass, take an old negative or a piece of opal, place a small portion of the lamp-black or soot in the center, and with a few drops of the gum-bichromate mixture, grind with an old palette knife or a worn out and flexible table knife. When the pigment is well ground up it should be removed by means of the knife to an old saucer, and thinned down to the proper consistency with some of the remaining bichromate and gum solution. I never weigh out any definite quantity of pigment, but after grinding add the gum and bichromate till I instinctively feel that the mixture is of the right consistency. The point at which the beginner nearly always goes wrong is in including too much pigment. This should be distinctly guarded against, and, instead of aiming at mixing an intense black liquid, the gum-bichromate solution should be added till the mixture is rather thin and easily workable with the brush. The right point will be reached when the pigment solution is of a slightly transparent greenish black color, which will allow the pencil marks on the paper to show through quite distinctly. After one or two trials, the beginner should experience no difficulty whatever with this part of the process.

For coating, the paper should be pinned down at the four corners to a board, and the sensitive pigmented solution applied by means of the brush. A good brushful should be sufficient to coat a whole-plate piece, the brush being worked backwards and forwards both ways of the paper till a thin and fairly even coat-ing is obtained. By this time the paper will have expanded slightly, and the pins should be removed from the corners and the sheet again pinned down. The coating, when dry, should appear fairly even and of a greenish tint; should any slight streakiness be observed, it can be ignored, as it will not be evident in the print after development.

Printing takes about the same time as that required for carbon, and a soft and thin negative is best for the process. If an actinometer of some description is used no difficulty will be found, after one or two trials, as regards exposure.

Development is effected by floating the print face downwards in a dish of cold water. It will be best at first to immerse the print face upwards, and after seeing that no airbells have formed, the print can be floated face downwards on the surface of the water and left till development is complete. If exposure has been approximately correct, development will proceed automatically, and may occupy anything between twenty minutes and two or three hours. In the case of over-exposure, the use of warm water will help matters considerably.

Using lamp-black as I have recommended, the resulting print will be of a pleasing brownish black color suitable for most subjects ; but should the reader desire a greater variety, he can gratify his taste by procuring tubes of moist water-color of the requisite tints, and using them in place of the lamp-black.

The Photo-American.