The first thing is to decide how much albumen has to be prepared to coat the quantity of paper required. As a guide, it may be mentioned that a ream of paper will consume 1 1/2-2 gal. albumen; and as one egg yields 3/4-1 oz. albumen, according to its size, it is easy to arrive at the number that will be required to coat a given quantity of paper, bearing in mind that more than is actually consumed by the paper must be prepared - sufficient to well cover the bottom of the dish when the last sheet is floated. Thus, a couple of quires of paper (a convenient quantity for an amateur to prepare, at a time) will take something like 1 qt. of albumen; this, on an average, will be obtained from about 50 eggs. If the paper be coated in the whole sheet, of course considerably more than this will be necessary; but for the nonce we shall assume that the paper will be prepared in quarter sheets, as that will be the most convenient size for the novice to commence with.
Fresh white of eggs can now be purchased in any quantity, the egg merchants finding it to their advantage to break the eggs and sell the albumen and yolks separately, as there is a large demand for. both, but for different purposes - the former for albumenising paper for photographic purposes, and the latter in the preparation of kid leather for the manufacture of gloves. Therefore, when the albumen can be conveniently purchased separately it will be found more economical. However, we shall assume that this cannot be done, and therefore the eggs must be broken by the operator himself. Here some little dexterity is required in order to avoid the yolk getting mixed with the whites. The best plan is to break the egg by giving it a smart tap on the edge of the cup, and then drain the albumen into it, retaining the yolk in the shell. By draining the white from each egg first into a cup, the yolk, if it be accidentally broken, does not get mixed with the bulk of the albumen. The yolks can, of course, be transferred to the culinary department.
It is generally recommended, in breaking the eggs, to separate the germ from the albumen, but this is never done in actual practice. With regard to the kind of eggs to be used, good ordinary French eggs will answer quite well, and they will be found practically as good as the more expensive "new laid." The requisite quantity of albumen being obtained, it is well stirred up, and to each quart, 300 gr. ammonium chloride, dissolved in the smallest possible quantity of water, is added. The whole must now be converted into a perfect froth. Unless this part of the operation be very perfectly performed, it will be quite impossible to ensure a perfect coating. Professional albumenisers usually employ an American churn for this purpose; but, on a small scale, the domestic egg whisk borrowed from the kitchen will answer quite as well. The whisking must be continued until the vessel containing the albumen can be inverted for a minute or two without any of the albumen draining out. The vessel is then placed away in the cool place for 3-4 days, according to the temperature, to allow the albumen to subside. By this time, it will have become very limpid. If the albumen be kept in a cool place, and the eggs be tolerably fresh when broken, it will keep the above length of time without fear of decomposition.
It could be used after a day's keeping, but it would be next to impossible to obtain a coating perfectly free from streakiness.
Some keep the albumen for a much longer period than that named - or until it has become quite putrid - before use, as then it is more easy to manipulate, and produces a finer gloss. We have been given to understand that dried blood albumen is sometimes added to thicken that obtained from the eggs, so as to obtain a still higher surface. The proportion of chloride recommended above will give 7 1/2 gr. to the oz. of albumen, and will, therefore, be suitable for a 60-gr. sensitising bath.
Leaving the subject of the albumen for a few minutes, it will be well to direct attention to the paper itself. It is tolerably well known that the 2 sides of a sheet of paper are different, one being very smooth, while the other possesses a certain amount of roughness, due to the web upon which it was dried in its manufacture. It is the smoother side which is to be albumenised. As the reams are received from the mill, the smoother side is always packed in the same direction; but when the ream is broken, and the paper sold in small quantities, it frequently gets mixed. Therefore it is necessary to examine each sheet separately, and in cutting it up - supposing it is to be prepared in less than whole sheet - to take the precaution that the smoother surface is arranged all one way, so that no mistake need be made in floating the wrong side on the albumen.
The albumen having stood the re-quisite time, it is now carefully strained; a fine cambric handkerchief will form a good medium for the purpose. After straining, the most careful albumenisers filter the albumen through a sponge; but this is scarcely necessary if the cambric be close in texture, and the albumen has been carefally decanted without disturbing the sediment. It is now poured into a dish of a suitable size, avoiding the formation of air-bubbles as much as possible. After standing for a short time, to allow any minute ones that may be accidentally formed to come to the top, the albumen is carefully skimmed by drawing a piece of blotting-paper along its surface. It is now ready to receive the paper.
In floating the paper, some little dexterity is required to avoid bubbles, and many operators have different plans of placing it upon the albumen. Some bend the paper in a curve and apply the middle first, and then gently lower the 2 ends. Others, holding it by opposite corners (diagonally), bend it, and apply first one of the free corners, gently lowering it to the other, and finally lower the 2 corners by which it is held. Many apply the paper in this way, and it is the plan we prefer: Holding the sheet by its 2 ends, they place one on the surface of the albumen at one end of the dish, and gently lower the remainder. By this method any air-bubbles, should they be accidentally formed, will be driven toward the end of the sheet, where they can easily be forced out by gently tapping the back of the paper with the tips of the fingers; whereas if any be formed when the middle of the sheet is applied first they are not so easily noticed, or expelled when they are.
When the paper is first applied - particularly if it be very dry - it will probably curl up and leave the albumen at the edges, but it will speedily flatten out again. It must not, however, be removed until it lies uniformly flat; otherwise the coating will prove unequal in thickness when dry. In practice it is advantageous to employ 2 dishes, and it will then be found that by the time the second sheet is floated the first one will have become flat and ready for removal, and thus time will be considerably economised. If the paper be floated for too long a time the albumen will sink deeply into it, and thus to some extent prevent a high gloss being obtained. (Brit. Journ. Photo.)