第32章
It often occurs that no trace of the image is as yet perceptible, but if the plate is heated by placing over a spirit lamp the unprepared side, or if left for some time in the dark, or, lastly, if exposed only a few seconds to a weak, dimmed light, the positive picture then appears with all its shades.
Of these three modes of bringing out the image, the second is superior to the others.
MANAGEMENT OF CHEMICALS.
It is necessary, first of all, to know that you have a chemical which is capable of producing good results when in skillful hands.
For this reason it is best to prepare your own quick, after some formula which is known to be good. Those quick-stuffs which contain chloride of iodine are noted for their depth of tone while they probably operate with less uniformity than those which are destitute of it.
For operating under ordinary circumstances, especially with an inferior light, probably no accelerator is more quick and sure than Wolcott's. It also produces a very fine, white pleasing picture, though lacking that depth of impression so much to be desired.
The dry quick operates with surety, and its use is simple and easy, producing an impression much like Wolcott's. For those having a good and permanent light, however, we would recommend a chemical giving more body to the impression.
There is a class of accelerators called sensitives, claiming to work in from three to ten seconds, which, however, will be found very little, if any, more sensitive than this. We frequently work it with the ordinary coating in twelve and fifteen seconds.
The manner in which the sensitives are worked is by coating very light.
In this way, a flat, shallow picture is obtained in a few seconds;and the same can be done with any of the more volatile quicks.
It is a fact not generally known, that a plate coated in a light chemical room is more sensitive than when coated in darkness.
By admitting a free, uniform light, and exposing the plate to it a few seconds after coating, then timing short in the camera, a very light, clear impression is obtained. The time in the camera is reduced in proportion to the previous action of light. The shades, of course, are destroyed, and the tone injured; still, for taking children, we have succeeded better by this method than by the use of "sensitives."The discovery of this principle was accidental, while operating where the direct ray s of the sun, entering the window just before sunset, fell on the curtain of our dark room, rendering it very light within.
The selection of iodine is not unimportant. Reject, at once, that which has anything like a dull, black, greasy appearance;and select that which is in beautiful large crystalline scales, of a purple color, and brilliant steel lustre.
Solarization, and general blueness of all the light parts of the picture, were formerly great obstacles to success, though now scarcely thought of by first-class artists. Beginners in the art, however, are still apt to meet with this difficulty.
It is occasioned by dampness in the iodine box, which causes the plate to become coated with a hydro-iodide of silver, instead of the iodide. The remedy is in drying your iodine.
If in summer, you can open your box and set it in sunshine a few minutes; or if in winter, set it under a stove a short time.
The true method, however, is to dry it by means of the chloride of calcium. It has such a remarkable affinity for water, that a small fragment placed in the open air, even in the dryest weather, soon becomes dissolved.
Take one or two ounces of this chemical, heat it in the drying bath, or in a hot stove, to perfect dryness; place it in a small glass toy dish, or large watch crystal, and set it in the centre of your iodine box.
Take this out and heat to dryness every morning. Adopt this process, and with your mercury at a high temperature, you will never be troubled with blue pictures.
Young operators are apt to impute all want of success in operating to their chemicals, even though the cause is quite as likely to be elsewhere.
Failure is quite likely to occur from dampness in the buffs, or in the polish;it is therefore necessary to be constantly on the guard in this quarter.
With a view to this, always scrape your buffs with a dull knife, or with one blade of your shears, the first thing in the morning, and after brushing them thoroughly, dry them, either in the sun, by a stove, or in the buff-dryer. It is equally important that the polish and the brush should be kept dry.
Want of success may arise from vapors of iodine or bromine in the camera box, mercury bath, or even in the buffs. It is incredible how small a quantity of these vapors will affect the effect of light when coming in contact with the plate, after or during the exposure in the camera.
It is therefore necessary to be cautious not to mix chemicals, nor open your boxes or bottles in your room, but take them out to do it.
Never hurry the operation through from lack of confidence in the result.
The fact of anything being out of order, forms no excuse for slighting the process. If unsuccessful, do not pursue the same course every trial, but vary with a view to detect the cause of the difficulty.
In case of a long series of failures, institute a regular course of investigation, after this manner, commencing where the trouble is most likely to occur:
1. Are the plates well cleaned?
2. Is the iodine dry? If the impressions come out blue, you may rest assured it is not. Take out the iodine, wipe and dry the box, and dry the calcium.
3. Is the quick battery of the right strength? If dry, it must change the plate in from six to fifteen seconds.
If any of the chloride of iodine class, it may vary from five seconds to a minute. Begin by coating light, and increase on each trial, observing the effect.
If the light side of the picture seems loth to come out, and shows no contrast with the dark side, it is to be inferred that your battery is too strong, and must be reduced with water or set out in the open air for a few minutes, with the lid off.