The yellow glass screen is prepared as follows: Take a piece of best plate glass—common cannot be used—clean it nicely; take another large plate glass, or anything that is level and true, level it with a small spirit-level. Now take the cleaned piece of glass and coat it with
| AURENTIA COLLODION. | ||
|---|---|---|
| Ether | 5 | oz. |
| Alcohol | 5 | oz. |
| Cotton | 60 | grs. |
The aurentia to be added to suit your judgment; it takes a very small quantity to make an intense yellowish-red collodion. Pour it on the center of the glass, flow it to the edges, and before it sets place it on the level glass and allow it to set; when set put it in a rack to dry.
Should it dry in ridges, the collodion may be too thick, and it must be thinned down with equal parts of alcohol and ether. A single piece of plate glass, about one-eighth inch thick, coated with aurentia collodion, is all that is required with an erythrosine plate. Or, after a piece has been successfully coated, another piece of the same plate glass, and the same size, may be cemented together with balsam, having the coated aurentia side between the two glasses; the edges may then be bound with paper.
In using different colored solutions, collodion, etc., I have found that one will change the focus and the other not. With some screens you must focus with them in their positions; take away the screen, and the picture appears out of focus. I cannot fully explain why it is, and for this reason will not make the attempt; experience alone can teach it.
Another thing that has been tried lately is to do away with the yellow screen by substituting a yellow coating direct on the plate. No doubt the focus on an object that requires absolute sharpness is somewhat affected by the use of a glass. We have been successful, on a small scale, to coat the plate with the following yellow solution:
Place in a tray enough of a saturated solution of tropæolin in wood alcohol to cover the plate; allow it to remain ten seconds. It is necessary that the plate should be bathed previously in erythrosine and dried. Before applying the tropæolin, which, being in alcohol, dries in a few minutes, have some blotting paper on hand, as the solution gathers in a pool and leaves bad marks on the end of the plate.
The plate can be developed in the usual way. Try it and see the results.—Reported in the Beacon.
Read before the Photographic Association of Brooklyn.