well defined the image may appear on the plate at this stage, it is never so clear as that a satisfactory plate could be engraved from it. It requires to be "intensified." To do so there are two methods that may be adopted, both of which have their advocates. One of these uses the bichloride of mercury as the agent, the other employs a solution of the sulphate of copper and bromide of potassium with nitrate of silver. The formula and operation with the first are as follows : Bichloride of mercury 2 ounces Muriatic acid 34 ounce Water 25 ounces Allow the plate to remain in this solution till it is bleached white, when it should be well washed in running water, and then flowed over with the following : Hydrosulphuret of ammonia s part Water 4 Parts This will make the plate an intense black. After being well washed it should be flowed over with a weak solution of nitric acid, in the proportion of i drachm to 4 ounces of water, well rinsed under the tap and set aside to dry. It should be mentioned that the bichloride of mercury is the well-known corrosive sublimate, a deadly irritant poison, and should be used with extreme caution.
The formula and operation with the other method are as follows : Sulphate of copper 25 grains Bromide of potassium 15 grains Water.... ounce Flow this solution while the plate is held in the hand. It will at first discolor or darken the film, but in a few seconds will bleach to white. After it has whitened through, let the tap flow over it till thoroughly washed, which will take about five minutes. The washing should be uniform all over, and if allowed to lie under the tap the water should be directed in an equal stream over all parts. It should then be flowed over with the following solution : Nitrate of silver 40 grains Citric acid 8 grains Ice or distilled water ounce Under this application the plate will blacken over, when it should be again thoroughly washed.
Clearing the is more than probable that it will not yet have been sufficiently cleared to print, in which case it should be flowed with the following solution of iodine : Iodine 40 grains Water 4 ounces with iodide of potassium added in small quantities at a time and shaken until all the iodine scales are dissolved. This will be of a deep brandy color. After allowing this solution to act upon the film a few seconds, it should be well rinsed in water under the tap, and flowed with a very weak solution of cyanide of potassium, which will instantaneously whiten over the film, and the image will be seen gradually to clear up. Great caution, however, is i needful in this operation. Should the cyanide be too strong, or allowed to act too fong upon the film, it will sweep away the dots in the shadows or cut away so much as to render the negative valueless. The tap should be kept running while operating with the
cyanide solution, ready to stop its action the instant it is seen to clear up. If an examination reveals that it is not yet sufficiently clear, the operation may be repeated. Should any part be seen to require clearing more than another, a small stream of the cyanide solution may be so poured from the graduate as to be directed on the clouded part without reaching the rest, though to do so will require delicate handling and much caution, as, a little overdone at this point, the whole negative may be spoiled. When seen by examination with the focusing glass to be sufficiently cleared with the cyanide, it should be again well washed, flowed with the foregoing weak solution of nitric acic, and afterward blackened with the solution of sulphuret of ammonia mentioned above, flowed again with the nitric acid, washed and set aside to dry. Wash well after flowing with all the solutions.
Features of a Good is to be hoped that the result of so much labor, necesitat ing so much careful handling, and the exercise of so much judgment, will be a good negative. If it is not satisfactory it will be but labor lost to proceed further, and it will be well at this point to describe what constitutes a good negative. Give it a minute examination under the glass. The darkest portions of the negative, which will be the high lights in the finished picture, should present a small, clear, transparent dot. The effect of the intensification should have been to close up the black dots which, after development, almost touched. If there are cross lines of white instead of the small dot, the high lights in the finished picture will be correspondingly dark and the whole effect will lack contrast and pluck. The black dots in the half.tones should vary in size down to the very small in the deeper shadows, and where strong contrast is wanted they may in some portions be down to nothing. Should the finished negative not present these features, it were better, in the spirit of nil dcsperandum, to throw it aside, and begin again at the beginning, hoping for "better luck next time." The Marginal resulting negative proving satisfactory, the further operations may be proceeded with, and the next, unless a vignetted effect is wanted, a marginal line should be run around the picture, giving it a finished appearance, and affording a guide for the router in mounting. With a square or straight edge laid along the margin of the picture, run the point of a graver along ; this will make a clean cut through the film, which will print black in the finished picture.