Developing The Image

There are two ways of developing - (a) By pyrogallic acid. (b) By proto-sulphate of iron. (a) To develop by pyrogallic acid, prepare the following bath: -

Distilled water . . • 100 parts Pyrogallic acid . . • 1 " Glacial acetic acid • . 10 "

When the plate is removed from the frame, take it by one corner, cover it with the above solution, agitate well the fluid over the entire surface, being careful that the plate is entirely covered with the liquid. The image gradually appears, but it is not very distinct; it is rendered perfect by putting it into a bath of -

Nitrate of silver .. 1 part Distilled water . . . 100 parts

When the image is perfect in all its parts, wash the glass with distilled water, and fix it.

(b) To develop by the proto-sulphate of iron, prepare the following bath: -

Distilled water . • . 100 parts

Proto-sulphate of iron . 10 "

Glacial acetic acid • . 2 " Sulphuric acid 2 drops

Filter, and pour it into a porcelain dish, and immediately plunge the glass in. In three or four seconds the image appears and is perfect Wash and fix it

Fixing The Proof

There are two methods of fixing the proof:

(a) By sulphate of peroxide of iron.

(b) By hyposulphite of soda.

(a) To fix by the sulphate of peroxide of iron, prepare the following bath: -

Distilled water .... 1000 parts Sulphate of peroxide of iron . 2 "

Allow the proof to remain in this solution from 50 to 60 seconds, wash with distilled water, and dry.

(b) To fix by the hyposulphite of soda, prepare the following bath: -

Distilled water . . . 1000 parts Hyposulphite of soda . 60 "

Operate as above.

Positives On Collodion

The principal advantage positive pictures possess is, that they do not reflect like the silver plate, and they require less time to take than negative pictures. The preparation of the plate for pictures is precisely the same as for negatives, except it requires a much shorter exposure in the camera. The pictures are developed with pyrogallic acid, to which is added a drop or two of nitric acid, or with the proto-sulphate of iron and the same quantity of acid. The two solutions are thus prepared -

I

Pyrogallic acid • . . 10 grains

Acetic acid . . • . 65 minims

Nitric acid 1 minim

Distilled water . . . 10 ounces

II

Proto-sulphate of iron . . 26 grains

Acetic acid . ... 80 minims

Nitric acid .... 2 "

Distilled water .... 640 "

What we have said above is sufficient to demonstrate the great utility of gun cotton in 12 photography, and the reader who wishes to make himself acquainted with the fall description of the manipulations of this art, can find them lengthily explained in Hardwick's "Man-ual of Photographic Chemistry." *

* This volume will shortly appear from the Industrial Press of Henry Carey Baird, Philadelphia.