Home >> Encyclopedic Dictionary Of Photography >> Acetic Acid to For Washed Emulsion >> Collodion Emulsion

Collodion Emulsion

alcohol, silver, water, added, tube, ounces, test and grains

COLLODION EMULSION (washed).—A plain collodion is first made up after the following formula : Alcohol, .82o 5 ounces Ether, .72o. zo ounces Pyroxylin 200 grs.

If a plain collodion, as sold by dealers, be used it should be remembered that the amount of bromide silver should be regulated according to the number of grains of pyroxyline in, and not according to the amount of collodion. As a rule, commercial plain collodion contains about 5 grains of pyroxyline to the ounce, after the addition of the iodizer.

To one-quarter of the collodion, or ounces, we must add too grains of zinc bromide. This is done by dividing the amount into two parts of 5o grains. One part is dissolved in a very small quantity of alcohol, and two or three drops of concentrated nitric acid added to it, and the whole is then added to the collodion. The other 5o grains of the zinc bromide is similiarly dissolved in the smallest quantity of alcohol, and five or six drops of the nitric acid added. This should be kept in a convenient test tube ready for use. We next take 165 grains of powdered silver nitrate and place it in a test tube with 2$ drachms of water. The test tube is then slightly warmed, when the silver should be completely dissolved, and when this is so, five drops of nitric acid are added to it. In another large test tube, or other convenient vessel, 3 ounce of alcohol .83o should be boiled and poured on to the silver solution. The two solutions are thoroughly mixed by repeatedly pouring them from one test tube to another. We have now the collodion, the zinc bromide solution, and the silver solution. With these we retire to a room lighted only by yellow light.* The collodion is placed in a large jar, and the test tube containing the silver is held in the left hand, and a glass stirring rod in the right. About three parts of the siver solution is then added drop by drop, vigorously stirring with the rod. The silver solution is then changed for the bromide, which is also added drop by drop. After this addition, the remaining portion of the silver solution is added. If any of the silver be found to have crystallized on the sides of the tube, it is redissolved in a little water and alcohol. After all the additions have been made, the emulsion which is how formed is briskly agitated to thoroughly mix the various ingredients, and a drop of the emulsion placed on a piece of glass and viewed by transmitted light. The color of a candle or gas flame should be of a deep orange

tint. A little of the emulsion on to a piece of glass is then carried out into the daylight, a little potassium chromate is dropped on to it, and it. should instantly turn a bright red color, proving silver to be in excess. The emulsion being satisfactory is decanted into a bottle capable of holding about 12 ounces, and well shaken up. It is then laid aside for twelve to fifteen hours to ripen. In about ten and a half hours it will have attained its maximum sensitiveness. It is now ready for washing. This is accomplished by pouring the emulsion into a large flat dish, so that its depth is not more than a quarter of an inch. The solvents will rapidly evaporate, and a skin will form on the surface ; this is broken up, and the emulsion well stirred up. This is repeated every now and then until the emulsion forms into lumps. It is then placed into a glass vessel and covered with distilled water. On the addition of the water some of the lumps will rise to the surface. Only a 'small portion of it should float, however. If much of it does, the evaporation of the ether and alcohol has been insufficient. If half a drachm of nitric acid be added to the distilled water freedom from fog will be secured. After a couple of hours the emulsion, or pellicle as it is now termed, is thoroughly washed in a running stream of water. A good method is to place it in a china or earthenware teapot. The lid is removed and a piece of fine muslin is tied over the top, and a stream of cold water sent down the spout for several hours.

The next operation is to remove the water contained in the pellicle. It is first transferred to a piece of muslin, and as much of the water squeezed out as possible. It placed in a vessel and covered over with alcohol. After about an hour it is again squeezed as before, and again covered with alcohol. At the expiration of another half hour the alcohol is drained off, and the pellicle is ready for emulsifying. If necessary it can be dried by a few hours' exposure to the air, and kept for future use in a dry state.

The moist pellicle is next dissolved according to the following formula : Pellicle... ioo rains Alcohol (.82o) 3 ounces Ether (.72o) 3 ounces A trial plate should be coated with this, as it may be necessary to dilute with more alcohol and ether.

The plates are then coated and dried.