The History and Practice of the Art of Photography

by Henry Hunt Snelling

To iodize the plate perfectly it must be placed over the iodine vapor immediately after buffing. Scatter from a sixteenth to the eighth of an ounce of dry iodine over the bottom of your coating box, and slightly cover it with cotton wool. The plate is then dropped into the frame b, fig. 12, with its silvered surface downward, and thrust under the lid h. The bright surface of the plate is soon coated with a film of iodine of a fine yellow color; it is then removed and placed over the accelerating solution. It is not absolutely necessary to perform this operation in the dark, although a bright light should be avoided. Not so the next part of the process, viz; giving the plate its extreme sensitiveness, or coating with the accelerating liquids. In this great caution should be used to prevent the slightest ray of light impringing directly on the plate, and in examining the color reflected light should always be used. A convenient method of examining the plate, is to make a small hole in the partition of the closet in which you coat, and cover it with a piece of tissue paper; by quickly turning the plate so that the paper is reflected upon it the color is very distinctly shown. Most of our operators are not so particular in this respect as they should be.

ACCELERATING LIQUID.--Of these there are several kinds, which differ both in composition and action--some acting very quickly, others giving a finer tone to the picture although they are not so expeditious in there operations; or in other words, not so sensitive to the action of light. These are adopted by Daguerreotypists according to their tastes and prejudices. They are all applied in the same way as the coating of iodine. The following are the best.

Bromine water--This solution is much used in France, and, I shall therefore give its preparation, and the method of using it, in the words of M. Figeau. "Put into a bottle of pure water, a large excess of bromine; shake the mixture well, and before using it, let all the bromine be taken up. An ascertained quantity of this saturated water is then diluted in a given quantity of distilled water, which gives a solution of bromine that is always identical." M. Figeau recommends one part of the saturated solution to thirty parts its bulk of water; but M. Lesebour finds it more manageable if diluted with forty times. In case pure distilled, or rain water cannot be procured, a few drops of nitric acid--say six to the quart--should be added to the common water.

Put into the bromine box a given quantity of this solution, sufficient to well cover the bottom; the plate, having been iodized to a deep yellow, is placed over it; the time the plate should be exposed must be ascertained by making a few trials; it averages from twelve to forty seconds. When once ascertained, it is the same for any number of plates, as the solution, which of course would become weaker and weaker, is changed after every operation, the same quantity being always put into the pot.

Chloride of Iodine.--This is prepared by introducing chlorine gass into a glass vessel containing iodine; the iodine is liquified, and the above named compound is the result. Operators need not, however, be at the trouble and expense of preparing it, as it can be obtained perfectly pure of Mr. Anthony, 205 Broadway, N. Y., as also all of the chemicals herein enumerated. The compound is diluted with distilled water, and the plate submitted to its action till it is of a rose color. Chloride of iodine alone, is seldom if ever used now by American operators, as it does not sufficiently come up to their locomotive principle of progression. The next is also eschewed by the majority, although many of our best artists use no other, on account of the very fine tone it gives to pictures.

Bromide of Iodine.--This is a compound of bromine and chloride of iodine. In mixing it, much depends upon the strength of the ingredients; an equal portion of each being generally used. Perhaps the best method of preparing it, is to make a solution in alcohol of half an ounce of chloride of iodine, and add the bromine drop by drop, until the mixture becomes of a dark red color; then dilute with distilled water, till it assumes a bright yellow. Put about half an ounce of this compound into the pot, and coat over it to a violet color, change the solution when it becomes too weak to produce the desired effect.

Another.--Mix half an ounce of bromine with one ounce of chloride of iodine, add two quarts pure distilled water, shake it well and let it stand for twelve hours then add twenty-five drops of muriatic acid, and let it stand another twelve hours, occasionally shaking it up well. Dilute six parts of this solution in sixteen of water. Coat over dry iodine to a deep yellow, then over the sensitive to a deep rose color--approaching purple--then back, over dry iodine from four to eight seconds.

Roach's Tripple Compound.--This is one of the very best sensitive solutions, and is very popular among Daguerreotypists. To use this, take one part in weight, say one drachm, of the compound and dilute it with twelve of water; coat over dry iodine to yellow, then over the compound to a rosy red. The effect in the camera is quick, and produces a picture of a fine white tone.

Gurney's Sensitive.--This is another preparation of bromine, and gives a fine tone. To two parts of water add one of the sensitive, and put just sufficient in the box to cover the bottom, or enable you to coat in from eight to ten seconds. Coat over dry iodine to a dark yellow, and over the quick till you see a good change, then back over the dry iodine from two to three seconds.

Bromide of Lime, or Dry Sensitive.--This is a compound but recently introduced, and is becoming somewhat of it favorite, owing principally to the slight trouble it gives in its preparation, and the tone it imparts to the picture. To prepare it, fill your jar about half or quarter full of dry slacked lime, then drop into it bromine, till it becomes a bright orange red. The plate is generally coated over this compound, after the iodine coating to yellow, to a violet, or plum color; but it will work well under any circumstances, the color being of little consequence, if coated from thirty to ninety seconds, according to its strength.