ALBUMEN PROCESS Negatives.—An old process invented by Niepce de St. Victor, in 1848. Glass was coated with albumen containing potassium iodide, and the film was sensitised by dipping in a nitrate of silver bath. Many modifica tions followed, but probably the process most widely used was the one published on May 21, 1855, by Mayan ; this comprised six distinct operations, as follow : (i) The albumen (white) of a fresh egg is beaten to a snow-like mass with a bunch of quills, afterwards dropping into it io drops of a saturated solution of potassium iodide and allowing to stand six hours at a temperature of 6o° F. (2) A piece of plate glass having smooth edges is cleaned by rubbing over it nitric acid with cotton wool, and polished with Tripoli powder moistened with a few drops of a concen trated solution of potassium carbonate. To the centre of the back of the glass is attached a pneumatic holder to serve as a handle. (3) The prepared albumen is strained through linen, and is then used to coat the polished side of the glass, this being placed on a level slab in a warm and dustlessp lace to dry. The glass is now known as the " iodo-albumenised " glass, and it will keep in a good condition for any length of time. It may be prepared in daylight. (4) The sensi tising mixture, or " exciting solution," is made by dissolving 5o grs. of silver nitrate in a mix ture of i oz. of distilled water and 12o minims of strong acetic acid, which operation and the following one must be done in a weak yellow light. Pour the sensitising mixture into a clean porcelain dish a little larger than the plate to be coated ; place one end of the albumenised glass in the solution ; with a quill, support the upper end of the glass and let it fall suddenly into the solution, lifting it up and down for ten seconds ; take it out, and place it face upwards in another dish half filled with distilled water ; allow the water to pass over the surface twice, take out and set aside in the dark to drain and dry. The plate at this stage is ready for expo sure in the camera, and will keep good for ten days if kept from the light, in a moderately warm place, and free from moisture. The sur plus sensitising solution may be filtered back into a black bottle for use again and again, adding occasionally a few drops of acetic acid and keeping in the dark. Exposure varies from four to ten minutes, according to light and stop. On a very bright day, and using the f/z6 stop, Mayall recommended an exposure of five min utes. (5) For development, the glass is placed film side upwards on a levelling stand, and a concentrated solution of gallic acid is poured over it ; the image takes from thirty minutes to two hours to develop. A temperature of io° higher than that of the room is advised, and if the image is feeble the plate is rinsed and covered with a solution of equal quantities of aceto-nitrate of silver and gallic acid diluted with water to half strength. This causes the
image to appear more quickly and stronger. The plate is next washed in three waters, and is then ready for fixing. (6) The fixing solution is made by dissolving 3 drms. of hyposulphite of soda in i oz. of water. The plate is allowed to remain until all the yellow iodide has dis appeared, and is next well washed and dried. " Success," said Mayall, when publishing this process in the Athenaum (No. 1,22o), " is sure to attend anyone practising this method, pro vided the eggs are fresh and the glass quite clean ; if the glass is not clean and the eggs stale, the albumen will split off the plate during the fixing." Among the modifications which followed for the purpose of quickening the plates were the addition of grape sugar, honey, and potassium fluoride, the latter proving to be the best of all. Malone's and other processes in use in the 'fifties of the nineteenth century differed in detail from the above, but in essentials were the same.
Positives.—At one time the albumen pro cess was widely used for the production of posi tives or lantern slides, and even at the present time, owing to the exquisite results obtainable with it, the albumen process is used by some of the largest lantern and stereoscopic trans parency firms in the world. It is hardly a pro cess for the beginner, because of the somewhat complicated formula and manipulations. The famous " Ferrier et Soulier " slides were pro duced by the albumen process, but the exact formula used was kept secret. Other formulm have, however, been published and worked successfully, the best being that in which the plate is coated first with collodion and then with iodised albumen ; the details are as follow : Pieces of good clear glass should be thoroughly cleaned by washing in a solution of 8 oz. of soda in z gal. of hot water, and rubbing well with rags tied to a wooden stick. Next, the plates are rinsed in plain water and placed in dilute hydrochloric acid (i in 2o). A sub stratum is next required, and this is made by mixing the white of one egg with 5o oz. of water ; the mixture being shaken up three or four times during the day and allowed to stand all one night, it is then filtered through fine muslin. The plates are taken from the acid bath, rinsed, drained slightly, and coated on one side with the albumen substratum mixture; next they are laid flat and dried. Great care is necessary to avoid dust and to get an even coating. When dry, collodionising and sensi tising may take place. Some ready-made iodised collodion is obtained (the longer it has been iodised the better), and the following solution is prepared : Distilled water . . 20 oz. i,000 ccs.