Photographic Reproduction Processes Part 12

MATT VARNISH.

Sandarac 6 parts Mastic 6 parts Lavender oil. 0.5 parts Ether 100 parts

When dissolved, add 30 parts of benzine. The opacity of the film varies with the quant.i.ty of benzine added; by excess the varnish dries transparent.

WATER COLORS WHICH RESIST THE ACTION OF LIGHT.

Red. Indian red. Light red.

Orange. Mars yellow.

Blue. Cobalt blue. French blue. Smalt. New blue.

Brown. Raw umber. Burnt sienna.

Green Terre verte.

Yellow. Cadmium Yellow Roman ochre.

yellow. ochre.

APPENDIX.

Although we intended to only describe the printing processes without the use of silver salts, we thought it would be well to complete this work by giving the most practical and interesting processes ever published to obtain permanent photographs; as they may give rise in the hand of experimenters to useful applications.

From time to time processes are published under "queer" names, which are based on the well known actions of reagents on the ferric salts reduced by light. They are derived from those described in the following pages.

We call specially the attention of the reader to the process of Poitevin, by which one can experiment with every ferric salts, citrate, lactate, oxalate, tartrate, benzoate, etc., by simply exciting with the corresponding acid. Observe that to obtain good results the paper should be strongly sized; it is a sine qua non, although not recommended by Poitevin.

C.J. BURNETT'S PROCESS(1857).

"A capital process for many purposes," says Mr. Burnett, "is to float or _steep_ the paper in a mixed solution of bichromate of potash and sulphate of copper, as for Hunt's chromotype process.(36) I have mixed gelatine, or occasionally grape sugar, or both with the solution;(37) but instead of developing it with nitrate of silver, as in chromotype, wash out the salt unaltered by light, and develop by floating on a solution of ferrocyanate of pota.s.sium. The purple red color of the copper salt which now forms the picture may be modified or changed in many ways,(38) viz., by soaking the picture, after the ferrocyanate of pota.s.sium has been washed out of the lights, in a solution of sulphate of iron. Solutions of gallic acid, tannic acid with alkalies of carbonate, may also be employed to modify or change the color. This process has the advantage that one may regulate the exact tone (black or useful neutral tint) to the greatest nicety by the time we allow the print to remain in the iron toning bath."

G.o.dEFROY'S PROCESS (1858).

Float the paper upon the following solution for three minutes and hang it up to dry:

Uranium nitrate 30 to 60 parts Silver nitrate 8 parts Water 100 parts

(39)

The sensitiveness increases in proportion to the quant.i.ty of uranium nitrate. With the above formula the paper can be exposed in the camera, or, for printing, under a negative cliche.

In printing an exposure of five seconds in diffused light gives an image perfectly visible, and a grayish black tone; ten seconds gives a vigorous image almost of a black color; in from fifteen to twenty seconds the image is very strong, with the color of an engraving. In sunshine the action is necessarily much more rapid.

The impression is developed by immersion in

Ferrous sulphate 8 parts Tartaric acid 4 parts Sulphuric acid 1 part Water 100 parts

The image is rapidly developed. It is fixed by washing in water.

DE LA BLANCHERE'S PROCESS (1858).

Uranium nitrate 25 parts Distilled water 100 parts

Filter the solution and keep it in the dark.

The paper should be sized with a gelatine solution at 5 per 100 of water, and, when dry, kept in the dark.(40) It is sensitized by floating five minutes.

The exposure under a negative varies from fifteen to twenty minutes in the shade, and from one to three minutes, at the most, in sunshine. As a rule, it is advisable to somewhat underexpose in order that the development be regular, progressive, under control.

The image is developed by floating, or immersion in

Silver nitrate 2 parts Distilled water 100 parts Nitrate acid, C.P. a trace

When the image is intense enough it is washed in several changes of water, then toned in a solution of gold at 1 per 1,000 of water acidified with traces of hydrochloride acid.(41)

The following bath develops slowly, and gives very rich purple tones without toning:

Nitrate of silver 3 parts Nitrate of uranium 1 part Nitrate of cadmium 1 part Alcohol 10 parts Water 100 parts Nitric acid traces

_The developing solutions should be as little acid as possible, but not neutral, for then the proofs would be veiled and grayish._

The image can also be developed in a solution of gold, or in a very weak solution of mercuric chloride at 1 per 10,000. The proof must be extremely well printed and left for from two to five minutes in the mercuric solution. If the time of exposure is right, the image will change but little in the solution, and will take, when treated with silver nitrate, the most splendid tones.

The proofs should be carefully washed when finished. If they were developed with silver, they must be immersed in diluted aqueous ammonia, which will perfectly clear the whites. If developed with chloride of gold, the water should be heated to 60 to 80 deg. C. (140 to 176 deg.

Fahr.)

HOUDOY'S PROCESS (1858.)

The paper is floated upon a lukewarm solution of gelatine at 5:100, and when dry, on a bath of uranium at 10 or 15 per 100 of water. After exposure to the sun the image is developed with a solution of silver nitrate acidified with acetic acid. The exposure varies, according to the nature of the negative, from one to ten minutes; it must be long enough for the image being developed in from thirty to forty seconds. It is then removed from the silver bath and placed in the following:

Ferrous sulphate 3 to 8 parts Acetic acid 2 parts Water 100 parts

In this bath the image takes a great vigor and appears entirely on the surface of the paper. When the proof has been too long exposed it should be washed slightly before placing it in the iron bath. Developed, the image is, generally, of a sepia tone, which can be turned to black by a solution of chloride of gold, 1:1,000, washing afterwards as usual.

NIePCE DE ST. VICTOR'S PROCESS (1859).