ORTHOCHROMATIC PHOTOGRAPHY

Scientific American Supplement, No. 711, August 17, 1889, by Various, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. ORTHOCHROMATIC PHOTOGRAPHY.

ORTHOCHROMATIC PHOTOGRAPHY.

By Oscar O. Litzkow.

What I want to show is the manner in which the process has been tested. My employer, Mr. Bierstadt, has given me permission to show you some samples, and also his chart containing the spectrum colors: violet, indigo blue, green, yellow, orange, red, and black. This chart has been photographed in the orthochromatic and also in the ordinary way.

There are many ways of producing an orthochromatic effect; one is the use of a glass tank placed behind or in front of the lens, in which a coloring matter from either a vegetable or mineral product is placed; this tank or cell is, however, only for use in the studio, as for outdoor photography we have a colored glass screen, so as not to be bothered with carrying colored solution.

The tank is constructed as follows: Procure two pieces of best white plate glass, about 6 inches square; between these place a piece of rubber of the same size square, and about 3/8 of an inch thick. In the center of this rubber cut out a circle about 4 inches diameter, and from one of the corners to the center of the circle cut out a narrow strip ¼ inch wide; this serves as the mouth of the tank. The two pieces of glass and the rubber are cemented together with rubber cement; then, to hold it firmly together, two brass flanges are used as a clamp, with four screws at an equal distance apart; a thin sheet of rubber is on the glass side of the flanges to prevent direct contact with the glass, the center remaining clear for the rays of light to pass through solution and glass.

One of the best orthochromatic effects made through this tank is with a three-grains-to-the-ounce solution of bichromatic of ammonia or bichromate of potassium. In this method there is no preparation used on the plate. A common rapid dry plate is exposed through this solution; the exposure, however, is about twenty times longer than it would be if you removed the tank with the yellow solution, or, in other words, if a dry-plate is exposed one minute without the yellow solution it would have to be exposed twenty minutes through a three-grain solution of bichromate of potassium or ammonia. It produces wonderful results on an oil painting or any highly colored object.

Another method, and the one best adapted for landscapes, is to bathe the plate in erythrosine and then expose it through a yellow glass screen.

As an illustration, suppose we have before us a beautiful landscape. In the foreground beautiful foliage, in the center a lake, in the distance hills, with a bluish haze appearing pleasing to the eye, also a nice sky with light clouds. Now make a plain negative, and see what has become of your clouds, hills, and the distance—not visible! Some photographers have been led to think that by underexposing they retain the distance, but they sacrifice the foreground; besides, it does not produce an orthochromatic effect.

But it is a good idea to expose longer on the foreground than you do on the distance. This can be done by raising the cap of the lens skyward and gradually shut off, giving the foreground more exposure.

Plates are prepared for orthochromatic work as follows: Take any ordinary rapid dry plate, place it in a bath containing

Rock it for two minutes, work as dark as you possibly can. Now take it out, and place it in the second bath for one and one-fourth minutes and keep it rocking. Have on hand for use a stock solution of

Prepare second bath as follows:

After removing the plate, dip it again face down to rinse off any particles of scum, etc., that may get in the bath accidentally. This bath may be used for one dozen 8 by 10, when it should be thrown away and fresh bath used.

After the plates come out of the last bath, they should be stood on clean blotting paper to absorb the excess of solution. I would also advise to use clean fingers. Pyro. or hypo. on the fingers is a drawback to success.

After plates have been drained, place them in a cleaned rack in an absolutely light-tight closet, with air holes so constructed as to admit air but no light; the plates will dry in from eight to twelve hours. They are best prepared in the evening, and, if the closet is good, will be dry in the morning.

After the plates are dry they may be packed face to face with nothing between them, in a double-cover paper box, and put in a dark closet free from sulphureted hydrogen gas, until ready for use. I have kept plates for three months in this way, and they were in good condition. Great care should be used in developing these plates, as they are sensitive to the red; get used to developing in a dark part of the dark room; occasionally you may look at the process of development in a little stronger light.

The exposure through the yellow screen with an erythrosine plate is about the same as if you had no orthochromatic plate—a plain plate instead—provided you are not using too dark a yellow on your screen. This can only be determined by experience. I will give to a common plate about four seconds, an orthochromatic plate under the same conditions five seconds.

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

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.

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