Chester F. Stiles

The name "carbon process" is a misnomer, as in this most beautiful of photo devices, we are not held down to a rigid set of tones, but may, by varying our coloring materials, produce any tone at will. "Pig-ment process " would more accurately describe it.

In the carbon process our work is more of a mechanical nature than chemical, and therefore our control over printing is almost unlimited. We simply dissolve away by warm water the parts of the picture not affected by light, and by varying the temperature of the developing bath in this operation, we can retard or accelerate at will. We are not, however, as was formerly the case, obliged to prepare these tissues ourselves, for several varieties, and all necessary colors are available at photo supply stores. This tissue, however, must be sensitized at home, as it does not keep well after sensitizing.

Before going into specific details we must briefly sketch the process in a general way. The "tissue," which iB the technical name for a piece of carbon paper, consists of a film of gelatine, into which pigments of the desired colors are incorporated. These pigments are minutely ground and are selected with the same care as artists' fine colors. The tissues are sensitized by the operator in a weak solution of bichromate of potash in warm water, after which they are dried for use. They are now sensitive to light and must be handled with more care than the ordinary ptinting-out papers.

Unlike the papers of the last-mentioned type, the carbon tissue does not show a visible image. The action of light is simply to render the gelatine insoluble wherever the light strikes - the eye can see no difference. In order to time the printing we have recourse to an "actinometer, " which we will later describe in detail. When the actinometer shows that the printing is complete, we remove the tissue in a semi-dark room, and develop the image by means of hot water.

A little thought here will show that the surface of the gelatine must be all insoluble because some light has been received by all portions of it. We are therefore obliged to work in from the back, and to do so must transfer the tissue temporarily to a support for development. This, of course, reverses rights and lefts, so when the development is complete another transfer may be necessary. In such an event we may, however, apply the tissue to a variety of supports-glass, paper, porcelain, wood, etc., making it the most versatile of all printing processes.

We would recommend that the novice in carbon content himself with the single transfer process. By selecting a negative which will bear right for left reversing ,such as a landscape, we may use the temporary support as a permanent one. We require the three dishes, one for cold water, one for hot water and another for a saturated solution of alum. Use dishes large enough to afford plenty of room and do not use rubber or composition trays for the hot water, for very obvious reasons.

The other materials necessary are some black varnish and a brush, a quantity of powdered alum, a few pieces of opal glass a little larger than the tissue used, a squeegee, and a board to operate on. For the varnish and brush may be substituted a ten-cent package of lantern binders to be used for making the " safe edge" on the negative, of which more further on. Opal glass is porcelain glass like the white opaque lamp shades. It is obtainable of glaziers and photo supply stores.

The sensitizing solution for carbon tissue is made by dissolving one ounce of bichromate of potash in 20 of water. This is an average formula, for in winter it is wise to make it somewhat stronger, and in summer, weaker. The bichromate is an orange salt which dissolves rapidly in water. Use hot water and filter while hot, so as to filter rapidly. Alcohol is added by some to the sensitizing bath to produce a quick drying tissue.

Use a deep zinc or porcelain tray and sensitize by immersion. Keep the pigment side up and watch for air bubbles on the surface. Authorities vary as to the length of time necessary in the sensitizer, but one to two minutes will usually be sufficient. Of great importance, however, is the temperature. Have this uniformly at a temperature between 50° and 65°.

After sensitizing, hang in a warm room where the tissue will dry quickly. The room should not be less than 70°, for tissue dried too slowly becomes insoluble in developing.

By means of the varnish we paint a border of black completely around the negative on the film side, or accomplish this same object by pasting on the lantern binders. After this the printing frame is made ready as usual, the operations being performed in very subdued daylight or by full lamplight. The pigment side is placed in contact with the negative, and another negative of as nearly the same density as possible is made ready with ordinary Solio paper in a separate printing frame.

The two negatives are placed in the sun together. When the silver paper begins to show detail in the dense parts, the carbon prints should be about finished. The tissue is then placed in the dish of cold water, care being taken to break all air bubbles which otherwise make spots. When the weather is dry the tissues will be dry and stiff; when damp they are much more limp. In case the tissue is dry, the cold water will end to roll it up. We must take care to keep the tissue under the water till it begins to flatten. The damper tissues do not need as much care and soaking.

The opal for the support being handy, we place the tissue upon it quickly, andjjsqueeze out all supei-fluous moisture and air. When this is done, the opal, with print upon it, is placed between blotters under pressure. In about five minutes it is ready for development.

The water for development should be at about 10° Fahr. The pigment commences to ooze out after a few seconds from between the opal glass and the paper of the tissue. When the proper time arrives the paper will strip easily from the tissue itself, but do not hurry this operation, for the tissue is delicate and will not stand forcing. In all this manipulation it is essential to keep the opal plate completely immersed in the developing water, so as to prevent tearing.