The American Carbon Manual/Many Mites from Many Minds
MANY MITES FROM MANY MINDS.
Be very certain that both of the varnished surfaces are perfectly dry before putting them together.
The sooner the tissue paper can be separated from the Saxe paper, in the tepid water bath, the better it will be for the picture; and, for this reason, never take into the tepid water bath more than a dozen pictures at one time, for fear they might soak there too long before they could be separated, and so, possibly, give trouble.
The “hydrocarbon varnish” (or India-rubber solution), and the “transferring solution” (or benzine), are very volatile and inflammable; should be kept tightly corked, to prevent waste from evaporation; and must never be used near a naked flame or fire.
The varnish brush, to be kept soft and straight, should be suspended from a hook on the underside of the lid, in a tin brush cup, which should always contain enough of the “transferring solution” to keep the brush saturated.
Pictures technically called “vignettes,” of the size of life, or cartes-de-visite, may be made on the tissue without difficulty.
The utmost care and attention must be used not to allow the tissue to be struck by light, after it is sensitized, either before placing it under the negative or in any of the subsequent manipulations. Remember that the sensitized tissue is much more sensitive to the action of light than any silvered paper, and that any want of care, in this particular, will certainly be punished by the entire failure of the whole operation. Several, who have used the tissue, have lost many pictures by neglecting this often-repeated caution.
As many prefer ascertaining the density of the sensitizing solution by the use of a hydrometer, instead of weighing the crystallized salt, and as the hydrometers in common use, unless of high cost, are not made with much accuracy or uniformity, it is recommended that each photographer who prefers to use the hydrometer, should carefully make one sensitizing solution, as herein directed, from the crystallized salt, and ascertain its density by the particular hydrometer he has in use. By this means, he may be sure of the strength of his sensitizing solution without the trouble of frequently weighing the crystals of his bichromate salt.
No definite time can be given for immersing the tissue in the sensitizing solution, because the time should vary with the season of the year and temperature. In warm weather, in summer, one minute, or even less, is sufficient; in a moderate temperature, in spring and fall, say a little less than two minutes; and in cold weather, in winter, three minutes. The only disadvantage from an unnecessary long time in the solution is, that it loads the tissue with a superfluous quantity of water, which requires too long a time to dry out or evaporate, and makes the tissue very tender. But the tissue cannot be “over-sensitized” (in the sense in which the term is used in sensitizing paper for silver printing), by too long immersion in the solution.
In making the second transfer, Mr. Swan recommends a solution composed of two ounces of gelatine, half an ounce of glycerine, and one pint of water. As it contains no sugar, it may, under some circumstances, be found preferable to the other formula.
Another sensitizing solution has been recommended, and is made by dissolving three ounces of bichromate of potash in thirty-five ounces of water, and adding strong ammonia until the solution becomes alkaline. Use litmus paper to test its neutrality, and when neutral add a quarter of an ounce of ammonia, to be sure that the solution is strongly, but not too strongly, alkaline.
It is recommended to all, to try it. It is thought, by some persons, to possess advantages over the other in rendering the tissue more flexible, and causing it to lay more closely to the negative. On the other hand, these qualities are disputed.
It has been found that good card-board sometimes answers a better purpose than the felt-cloth, in making both the transfers. It is, therefore, suggested to all to try it; but, where card-board is substituted for the felt-cloth, it is obvious that the press and rollers must be true, and work with great accuracy.
In making “vignettes,” twenty-five or thirty grains of chloride of barium may be added to every ounce of gelatine employed in the gelatine solution, which, on coming in contact with the tannin solution, will be converted into sulphate of baryta, and will give more clearness to the white background.
It is a good plan, though not very important, to filter the sensitizing solution.
The solution of gelatine should be filtered, while hot, through fine linen cloth.
It is best to make the first transfer, and develop the prints, soon after lighting, otherwise, they may sometimes become partially or wholly insoluble. As a general rule, the tissue may be lighted in the morning and the pictures developed in the evening; but, occasionally, from some unknown cause,—it has been known to occur but once in two years—the tissue, after having been lighted under a negative, will become insoluble if kept too long before being transferred and developed.
The last transfer may be made by pulling apart with the fingers, without the application of “transferring solution” or benzine, if the prints are allowed to dry twenty-four hours after the last pressure.
The clothes-pins used should always be clean.
The tissue is better dried quickly, but artificial heat must not be used to hasten it. Hang it, if possible, in a draught of air or well-ventilated room.
It is a good plan to take a sponge or soft brush saturated with water, and remove any adhering bichromate solution from the back of the print while it is drying, and take care not to touch the blackened surface. This will prevent the appearance of insoluble spots in developing. Thoroughly shake the sensitizing solution before using.
Don't put too many sheets in at a time.
If you make a stock solution of bichromate, keep it well corked to prevent evaporation.
Sometimes, in coating the print with the gelatine solution, there is a disposition manifested by it not to adhere on all parts of the surface of the print, but to “creep” off in certain spots. When this happens, there can be no adhesion at those points, between the gelatinous coating and the pictures; consequently, the film, composing the picture, will be torn off from such places, when the rubbered Saxe paper is removed. To avoid this non-adhesion and “creeping,” it is best to coat the prints in a warm room, where the hot gelatine will not chill nor " creep," upon being brought in contact with the surface of the print, as it would do if the print were in a cold apartment.
In preparing the moist paper to place the print upon for the final transfer, first soak it thoroughly in water, and then blot off or press off all that is free.
There is no difficulty whatever, in avoiding blisters in developing the prints; all that is required is, first, that the caoutchouc paper and solution for coating the tissue be prepared with highly volatile solvents (such as rectified benzine, and probably the very lightest of the spirit from petroleum, will answer equally well); any of the less volatile hydrocarbons remaining mixed in small proportions with the lighter through imperfect rectification, are mischievous. Second, the proportion of caoutchouc in the solution and on the paper, should not be too small. Third, heavy pressure must be applied after the tissue is laid down on the caoutchouc paper: this is most important; that is to say, if the tissue and paper are laid together dry, if I may use the term. Of course, if the caoutchouc solution, or the tissue, or paper, is fluid when they are brought into contact, air can be excluded, and perfect cohesion obtained without pressure, but then a long time must be allowed for evaporation of the caoutchouc solvent. But probably the dry method will be preferred, and with that method strong pressure is indispensable, in order to avoid blisters. Fourth, in developing the prints, the paper on which they rest must be carefully handled, so as to avoid creases and rumples. Wherever a crease or incipient break in the paper occurs, there will be a blister. Fifth, avoid the use of very hot water. To that end, use tissue easily soluble; that is to say, tissue which is fresh, and that has been so quickly dried as to retain the normal solubility of the gelatine almost unimpaired.
When removed from the bichromate solution, if the back of the tissue be drawn over a glass rod the superfluous solution will be removed, and prevent insoluble spots in the print.
Never be in too great haste. Follow the given rules, and you will succeed. Cleanliness and care are quite as essential in this as in the silver process.
Remember that bichromate of potash is quite as poisonous as cyanide, and, getting it into cuts and abrasions of the skin, should be avoided.
Bubbles and blisters, in the tissue, arise from the presence of air in the pores, which suddenly expands when the tissue is suddenly placed in hot water, and swells into bubbles under the film of India-rubber. If the tissue is immersed for a few minutes, first in cold water, previous to development, face up, the air is expelled by the water in minute globules, and blisters avoided.
Do not be in too great haste to separate the picture.
The immersion in water also removes the chromate from the paper, which thus becomes insensitive to light, and permits the development to be made in the daylight.
It is not found best to use a brush on the surface of the newly-developed print. It endangers the whites. Moving it dexterously back and forth in the water, face up, will remove all the superfluous carbon.
Better to gradually increase the temperature of the water during development, than to have it too hot at first, and have to decrease it. Do not, however, increase the temperature too rapidly, or uneven development and blisters will occur.
The addition of half a drachm of balsam of fir to the pint of “hydrocarbon varnish,” shaking it repeatedly during the day, will secure greater adhesive qualities.
The felt cloth used should be thick, of close texture, and soft.
Mr. W. J. Kuhns announces, that by simply washing the print with aniline colors before transferring, almost any tone or color may be given the print, and with beautiful results.
Liesegang recommends protecting the prints with a thin film of plain collodion.