Fig. 104

358 Second Preparation 126

There is another kind of dryer made by Mr. S. Rogers, described in the almanac of the British Journal of Photography for 1870. As Fig. 105 shows, a burner, c, furnishes a current of hot air, which follows the direction indicated by the arrows. The air in the jacket, A D B', which surrounds the tube, c a' is heated by the combustion of the burner, c; it enters from above into the dryer a a by an opening made in the side B and a'; thence it passes in, descending over all the horizontal separations which are arranged in such a manner as to receive in all their length a current of hot air. Having reached the bottom it makes its exit by an opening leading directly into c, and by increasing the current materially aids the combustion. The exterior air enters the bottom of the jacket by a small opening at a. The ammonium and ten grains (0.625 grammes) of chloride of calcium are added; finally, after everything has dissolved, an ounce (30grarm ordinary sprits of wine is added, and the mixture filtered. The filtered solution is poured upon the warmed glass plate, and spread over the surface by means of a strip of paper.Not too much, nor too little liquid must be applied, but only so much that when the pi inclined only a little of it betrays a tendency to run off When the operation has been carried out several times , the proper amount to be applied is easily guessed..

Fig. 105.

358 Second Preparation 127

Too thick a film does not last in printing, as the scraper abrades the surcloset of the dryer is furnished at the bottom with adjusting screws, so as to permit the levelling of the interior separation at one operation. - Leon Vidai..

2.Gelatin,.........................

1 ounce.

Bichromate of Potash,.........................

70 ounces.

Water,.........................

20 ounces.

In winter from 10 to 20 drops of glycerin may be used. Soak the gelatin in 10 ounces of water for an hour, then add the remaining 10 ounces of water and the bichromate of potash. Heat to 100°, stirring until dissolved; then filter several times, and it is ready for coating the plates. When warmed to 100°, the plates will dry in ten to twenty minutes. Then cool off •lowly, and they are ready for

3.Gelatin,....................

1 ounce.

Russian Isinglass,....................

3/4 '

Water,....................

24 ounces.

Alcohol,....................

4 "

Bichromate Ammonium,....................

90 to 120 grains.

Calcined Magnesium,....................

10 to 20 "

Chrome - alum Solution,....................

1 to 2 drachms.

Dissolve the isinglass in 6 ounces of water by boiling from one to two hours, and the gelatin in 8 ounces of water, in water-bath at 100°, and add the alcohol and remaining chemicals to the remaining 10 ounces of water, except the chrome - alum solution, which should be added last, and on the day of use only. Do not raise the heat in any case above 120°. With solution No. 3, coat the plate precisely as with No. 2, except that the solution should flow off the opposite corner. Let the plates stand for a few hours after they are removed from the oven, and then expose under the negative to diffused light the proper time. The chrome - alum solution is made as follows:

Chrome-alum,.........................

40 grains.

Bicarbonate of Potash,.........................

20 grains.

Water,.........................

5 ounces.

" Artotyper."

Professor Husnik's method of making a substratum on the glass plate for the gelatin film is an excellent one, and the best so far published; hut it has been improved (and this is the method adopted by the Artotype Company) by drying the film at once in the oven used for drying the gelatin film, at a temperature of about 160° P.; this enables the plate to be used at once for the gelatin, the heat causing the mixture of silicate of soda and albumen to coagulate in less than half an hour and adhere very firmly to the glass. The best oven face; and too thin a film, on the other hand, permits the fine grains of the glass to appear as little black spots, the force employed in the press being the greater. When coated, the plates are put into the box and allowed to dry at a temperature of 35° R. Plates prepared to this stage will keep good in summer for the space of a week, and in winter-time for a month, becoming better after keeping a little while.

for the purpose (and the one used by them) is made by simply making a simple wooden box, about thirty inches square and five feet high, the bottom formed by a closed, flat, hot-water pan, made of metal, about four inches deep, and having two pipes leading outside, one for the escape of steam and one to pour water into. A gas- or kerosene-stove is put underneath, and, if it has been carefully levelled, two thicknesses of blotting-paper are put on top of the pan, on which the plates are to be laid. Several more rows of glass can be put in by means of strips laid across at intervals, with levelling-screws attached. One side of the box is a door. The drawing will give something of an idea. The albumen and silicate solution should be carefully spread over the cleaned surface of the plate (in a room absolutely free from dust), the excess allowed to run off, and then laid in the oven at a temperature of 140° to 160°, and allowed to remain about twenty minutes or one-half hour. It is better to keep these plates a day before using, but when dried this way, they may be used at once. They must then be rinsed under a tap and dried again, when they are ready to receive the gelatin. The oven must be brought up to at least 180°, the plates carefully levelled, and then the gelatin mixture is to be applied, by pouring on in the centre until it just spreads to the edges of the glass, but no more; experience is necessary in this. The method now practised in Europe is to pour off the excess, and pour on again, and then pour off all but a little of the excess, and allow to dry. This avoids any air-bubbles, and also too thick films. The thicker the film, the coarser the grain, and more intense the blacks. The thin films give the best detail, but too thin ones yield flat prints. The Artotype Company (and so does Albert) replace about one-third of the gelatin with Russia isinglass, which is belter than pure gelatin; the latter must be of the kind known as the "Magdeburg" a German make, which does not swell much in water. The plates will require about twenty minutes to a half hour in the oven, and during this time the door should not be opened. As soon as dry, they are ready for exposure; this must be learned by experience, and varies with the negative. After exposure, it is washed thoroughly under a tap till all the unreduced chrome-salt is washed out, and again dried, when it is ready for the press. I wish here to remark, that the Russia isinglass requires to be boiled two or three hours, and then the insoluble residue must be separated from the solution before adding to the gelatin. It is also unnec-essary to grind the glass, as recommended by Professor Husnik. It will also be found better to dry the gelatin film at about 200° F. than any lower; the high temperature gives a finer grained film. In order to produce a larger number of impressions from a plate, several modes of hardening (notably with chrome-alum) have been patented, but it is not meet with success if he possesses taste and knows what a good print is. In order to guide the printer, it is well to place before him a good print, made with chloride of silver on albumen, from the negative which has impressioned the gelatin film. He will there find all the value of the negative, and it will be easy for him to know if he is to use more or less ink, in order that his print should resemble, as much as possible, the one made with the silver salt. This is a question of care and taste rather than of skill. If the time of exposure to the light has been suitable, the printing will necessarily be good. It is important to note that it is very difficult to obtain, in the blacks, the transparencies that exist in the albumen print. The fatty ink when dry is mat, and it is only by passing a varnish on the surface that it is possible to preserve the transparency of the strong shades. The character of the cliche used naturally plays a very important part in view of the result to be obtained, and that is the reason that it is difficult for the printer to know what he can obtain from his plate, if he does not have before him a print made from the cliche. As soon as the operator has obtained a print which he thinks to be as good as possible, he should place it alongside of him, as a type, to serve as a comparison with all the other prints as they are successively made. By this means he will discover if too much ink is used, or if there is too much hardness, and it will be easy for him to correct these faults, either by hardening the ink on his table, or by adding to it a small quantity of varnish to render it harder and more suitable for producing the half-tones. If, notwithstanding this last care, very decided whites should show themselves, he must conclude that the gelatin is too moist, that it has absorbed too much water, and he should stop the printing in order to allow a portion of this excess of moisture to evaporate, unless the defect be the consequence of under-exposure to light, which is irremediable. If, on the contrary, the print be too black; if the half-tones are too heavy, even with very hard ink, it is because the plate lacks moisture, or that there has been over-exposure to light. In this case the saturation of moisture should be increased by adding to the water a very small quantity of ammonia, or else a few grammes of ox-gall.