Manner Of Spreading The Gelatin On The Plate. First cover the plates which are to receive the gelatin with a thin coating; of albumen:
White of Egg,..........................................
to which you add a solution of chrome-alum in sufficient quantity to impart a rather dark-bluish tint. Allow this first coating to thoroughly dry, often putrefy, and then it becomes a fluid of its own accord, and loses the power of solidifying. This can be prevented by adding from one to two per cent, of salicylic acid or of thymol dissolved in five cubic centimetres of alcohol for every one hundred cubic centimetres of gelatin. Separation of the film from the glass during development, formation of bubbles, protrusion of the layer of gelatin over the edge of the plate, production of creases, distortion and tearing of the negative image - all these defects are due to the employment of too soft a gelatin; by using collotype gelatin they may be avoided. The same effect is produced when the emulsion contains a considerable amount of gum-arabic. It may be cured by cleaning the glass with a weak solution (1: 200) of soluble glass, which causes the gelatin to adhere more firmly; coating the edges of the plate with a varnish of caoutchouc is also a remedy. A complete cure is obtained by, previous to developing, dipping the plates for about five minutes in a saturated solution of alum in water, followed by thorough rinsing. According to Chardon, it suffices to dip the plates in alcohol, and only to develop afterwards. Light-colored spots, without any sharp outline in the negative, may be attributed to some fatty substance in the gelatin; the spots may be got rid of, and the silver bromide plates rendered homogeneous, by filtering the gelatin several times through filter paper. - W. P. Bolton.
329. For coating and drying plates my levelling - board is three feet by two feet and six inches, one and a quarter inch thick, with two stout battens crossways of the wood underneath. This requires to be pretty stout and rigid, and made of good dry timber. Across the surface there are fastened strips of wood half an inch square and at three-inch intervals. These are simply guides in the process of levelling: a lid, made as light as possible, but light-tight, and of sufficient dimensions to cover the entire board, with a flange sufficiently deep (say three Inches) to cover the board-plates and for the lower edge to rest upon the table.
To level the plates, make a lot of little common clay cylinders by rolling the clay into lengths of a few inches and about half an inch in diameter, and cutting it up into about three - quarter inch lengths; three of these pieces of clay are used to each plate. The pieces of clay are placed on the leveller's board at such a distance as to suit the size of plate, and on each piece of clay I press a gun-wad; upon these the glass rests. A circular spirit-level, or two ordinary spirit - levels placed at right angles upon the plate, enables you to see which way the plate requires pressing down upon the clay supports to set it perfectly level. I have tried all sorts of means of levelling the plates, but find this the best and most simple; a little then spread over it by the aid of a bent glaas rod the gelatin emulsion, which has first been dissolved over a water - bath at a very moderate heat, and in ten per cent of ordinary water slightly alcoholized. Some add to the emulsion a small quantity of chrome-alum to preserve the adherence; others, a few drops of ammonia to increase the sensitiveness. Thoroughly practice will enable you to level the plates rapidly and perfectly. I never exceed half an hour in levelling sixteen plates.
Coating the plates: During the time I am levelling the plates. I have one of the pots of emulsion placed in some hot water in the " laving can " over my gas - burner, with just sufficient gas to keep the water hot, but not to boil - say at a temperature of 130° or a little more. By the time I have levelled my plates, the emulsion will be melted and heated up to the same temperature as the surrounding water. Now commences the dark-lantern business. My lantern is a wooden box, twelve inches every way, the front consisting of two panes of glass, which slide in grooves, and are sufficiently long to be easily taken hold of and lifted out The one glass is ordinary sheet, coated on one side with negative varnish, containing a sufficient quantity of aurine to make it a tolerably deep yellow; the other glass is ordinary ruby. The slides are arranged to leave one inch space between the two glasses; a parafflne lamp is placed inside the box, which is provided with a good - sized chimney, such as are used for magic lanterns. The yellow glass is nearest the light, and the ruby outside; this gives plenty of light, is perfectly safe, and about as cheap and convenient as anything you can get proceed to filter the emulsion through a good tuft of cotton-wool placed in a funnel. Place a glass marble upon the cotton-wool in the centre; it prevents the wool rising when the emulsion is poured upon it. Before pouring the emulsion on, pass some hot water through the cotton-wool, and pass the emulsion through twice, at least gelatin is to dampness, how the least change in this respect will change the nature and the action of gelatin in any form.And when it is sensi-tized, the light coming upon it will spoil it instantly. Dry air and freedom from light coming positively essential to success.
dry in a current of air, and where there is no dampness. You will now have sensitized plates of excellent quality, ready to be used or packed away. These plates, carefully packed, may be indefinitely kept, as well as the emulsion, but, like the emulsion, they must be protected from dampness and light. Remember, in all your manipulations, how very sensitive
The pouring - bottle consists of a blue pyro bottle, close to the bottom of which I have bored a hole, and into this hole 1 introduce a glass tube, with a portion of India - rubber tube upon it to make it water-tight, and tie a string round the tube and neck of the bottle to hold the tube in its place. This is my pouring-bottle. You will see my object is to pour from the bottom, thus avoiding air - bubbles. The tube is simply a " feeding - bottle " tube, and the whole thing does not cost a shilling, but is worth a good deal for this job. Heat the bottle in warm water, filter the emulsion directly into it, and set it in a basin of hot water for immediate use.