The Enameling plate being well polished, it is now ready to receive the enameling solution. For this there are various formulae, each supposed to have merits of its own, and hedged around with all the importance of mysterious secrecy; but the bases of all is a glue or gum, preferably Le Page's fish glue, which is now specially refined and clarified for the purpose, while the sensitizing element is the bichromate of ammonia. To these most operators add a proportion of albumen, and the varying proportions of these ingredients constitute the virtues of the so-called secrets. Some, however, discard albumen, and as the presence of this prevents the keeping quality of the solution, it should only be made up in small quantities for early use, or not more than will suffice for a week or two's work. That made without albumen may be made up in larger quantities, as it will keep indefinitely; but it necessitates more careful washing out after development, the albumen, when used, washing out more readily. We give both formula, that the operator may take whichever, after practical experiment, he is most successful with.
Le Page's clarified fish glue z ounces Bichromate of ammonia r 20 grains Albumen 2 ounces Water 6 ounces The whites of four eggs of medium size will yield the above quantity of albumen, which take, carefully excluding the yolk and the germ, and thoroughly beat up and set aside to settle. Grind the bichromate with the water, mix with the glue, and add the albumen, and beat up the whole again. A common domestic egg-beater is very suitable for this purpose. Make the mix ture up in non-actinic or feeble light, and set aside for several hours, when it should be filtered through a small piece of fine sponge in a large funnel, and put into a stock bottle, and again filtered in the same manner before using.
The formula without albumen is as follows : Clarified fish glue. 3,4 ounces Bichromate of ammonia So grains Water to ounces The directions for making giving above will apply equally to this. They should be tested with litmus paper, and will more than likely be found acid. Neutralize with a few drops of concentrated ammonia.
Sensitizing the Metal plate having been cleaned and polished, let water from the tap freely flow over it, and, slightly draining the surplus, pour a portion of the solution on at the upper right-hand corner, when it will sweep the water from before it. The solution will have been filtered through a sponge and convenient at hand in the graduate. Flow a second and a third time. Let the surplus at the first flowing run into the sink ; if that of the succeeding flow ings are thought worth the saving, do not catch them in the graduate from which the solution was poured, but in some other, because so doing will cause air bubbles to form, which will be sure to cause trouble afterward. At the last flowing retain enough to flow back over the plate,
and, keeping it in a level position put it into the " whirler," and whirl, at first with a slow motion, and gradually increasing in rapidity for a minute or so, when it should be examined for any specks or air-bubbles that may appear on the film. If there are any seen it is a misfortune; should they be air bubbles, they may be pricked with a needle, and in the after flowing they will disappear ; but if they arise from dust the easiest way is to polish over again and begin from the bottom. These specks are sometimes unaccountably troublesome, and may result from acidity of the solution, so that it is well to prove it with litmus that it is in a neutral condition ; if from air bubbles, the best preventative is to keep the point of the funnel through which the solution is filtered resting on the bottom of the graduate ; if they are from dust, it is obvious that the room requires sweeping out, or even the floor mopped and washed out, and to remember that cleanli ness is an essential to success. If there are no such manifestations, flow again with the solution, and this time let the whirler be so arranged that a gentle heat may be applied, so it may be dried as quickly as possible. This may be conveniently done by holding the whirler over a gas stove, or other cleanly heat, and whirl in the same manner as before, which should take about three minutes. Care must be taken, however, not to expose_to extreme heat—indeed the less the bet ter—otherwise the albumen may become coagulated, in which condition it would not wash out in development. The plate may now be set aside to cool, and others coated and sensitized, or made ready for printing. Of course, the coating of the plate, it will be understood, is to be done in the dark-room, or With subdued light, and until time of printing set in a dark cupboard or other receptacle.
The whirler may be of any form that will impart to the plate a rapid circu lar motion, the idea being to obtain by centrifugal action a perfectly equal distribution of the solution over the plate. Perhaps the simplest form of whirler we have ever known being used was that of a cord suspended over the stove, and twisted till the strain, on being relieved, gave the desired motion, on the principle of an old time cook's.