ON THE USE OF PYRO-GALLIC ACID IN PHOTOGRAPHY
The Chemist, Volume 1, 1849-1850
Brief
BY J. S. ARCHER, ESQ.
PDF Page 371
THE proposed employment of a layer of albumen on glass as a substitute for paper having given a new impulse to the photographic art, tending to produce a surface which bids fair to rival the daguerreotype plate in the delicacy of its delineation and in the sensibility of its surface, induces me to call the attention of those engaged in photographic pursuits to the use of pyrogalllic acid to develope the latent picture.
Although gallic acid in combination with the ioduret of silver produces a very sensitive surface, it is, in this respect, far surpassed by pyro-gallic acid.
During the last summer I used this acid with considerable success, its action being both rapid and sure.
The proportions I took were as follows:
- 40 grains nitrate silver dissolved in about the same quantity of water, to which is added
- 1 oz. of glacial acetic acid grains of pyro-gallic acid dissolved in 1 oz. of acetic acid.
- 4 grains of pyro-gallic acid dissolved in 1 oz. of acetic acid.
Equal parts of the above solutions are mixed, applied to the iodized paper and at once exposed to the action of light.
The length of the exposure and the time necessary to develope the picture of course depend upon the power of the light at the time; these are points however which a little experience will soon decide.
There is one advantage in the above preparations, that no second wash is necessary to bring out the picture.
I may also remark, that the more acetic acid and the less water, are used, the better, in the preparation of the nitrate of silver and pyro-gallic acid solutions for producing the sensitive surface; for this acid seems to have the power of, in a great measure, preventing spontaneous change.
I need not say that a surface so sensitive as this will not keep.
If on mixing the acetic acid with the nitrate of silver any acetate of silver should be formed, a small quantity of water must be added to dissolve the same.
Care must be taken that the pyro-gallic acid is quite pure, otherwise the light of the picture will be discolored.
The acetic acid also should be quite pure.
ON THE USE OF PYRO-GALLIC ACID IN PHOTOGRAPHY
BY MR. FREDERICK SCOTT ARCHER
PDF Page 461
In my first short communication respecting the use of pyro-gallic acid in Photography (see THE CHEMIST, No. VIII, May, 1850, page 30), my intention was merely to introduce it as a powerful agent in developing the latent picture. I then said nothing respecting the best mode of proceeding so as to ensure success, merely giving certain proportions of the salts to be used, as a sort of introduction; but as it appears not at all unlikely that many will throw the thing aside as a failure from not taking certain precautions in the mode of operating which are necessary to obtain good results, I have thought it advisable to offer a few remarks on this part of the subject.
In the first place I must repeat what I said respecting the purity of the pyro-gallic acid, as this is a most important point to be attended to, otherwise a spontaneous change will be set up immediately the sensitive solution is applied to the iodised paper. The pure arid should be perfectly white, having & slight odor similar to that of balsam, and which arises, I should imagine, from a small quantity of empy-reumatic oil, which may be in itself an impurity, although I am not aware if there is any mode of separating it from the acid; this odor is variahle in different samples.
The formula. I gave for the sensitive solution will answer very well if the solution of pyro-gallic acid is used within a day.
In practice I have found it better to make only two or three drachms of the solution of pyro-gallic acid at one time to avoid this evil of decomposition: I will howerer suggest another mode of proceeding to prevent disappointment in this respect:—
Prepare the solution of nitrate of silver, 20 grs. to l oz. of acetic acid, and instead of the solution of pyro-gallic acid, add & very small quantity of the acid in powder to the aceto-nitrate when wanted for use; thus, all risk of change will be avoided, the acid will dissolve directly in the aceto-nitrate solution by stirring it with a glass rod, and is ready for immediate application: in this way also a larger proportion of the pyro-gallic acid can be used if it should be thought desirable to obtain the picture with greater rapidity.
The most important point to consider, next to the purity of the chemical solutions, is, the form of Camera best adapted to operate with success in the open air, for as soon as the paper is made sensitive to light it must be used. This a difficulty which it is most desirable to overcome, and I regret that in a paper like this, it will be almost impossible to give a clear description of what I should propose, more particularly as drawings cannot be given; however, by throwing out one or two hints respecting what is necessary, I cannot doubt that the best form of construction for the camera will readily suggest itself.
In the first place it is necessary that a slit (which may be, for a large camera, 1 inch wide and 3 inches long), should be cut in the top of it, midway between the back and front, into which a slip of yellow glass is inserted, and having a small hinged eover adapted to it, so that a small quantity of yellow light may be admitted into the cunera when necessary. The upper right hand corner of the front of the camera should be cut oft, and an elastic tube, about 2 inches deep, fixed on the opening, made just large enough to fit the socket of the right eye, with a cover to it, on hinges, shutting from the inside; a piece of glass mnst be cemented at the bottom of the tube to prevent the vapor of acetic acid injuring the eye.
There should be an opening on the right hand side of the camera, sufficiently large to admit the hand of the operator when he wishes to prepare the sensitive paper; this opening must have a tube, made of silk, about 12 inches long, fitted to it, and gradually diminishing towards the end, into which an elastic band must be sewn, to enable it to adhere close to the wrist to prevent the admission of light; it will be advisable to have a similar opening on the opposite side of the camera.
A water bath is placed inside the bottom of the camera, with a jointed cover, water tight, into which the paper is plunged immediately the negative picture is devel-oped, in order to prevent any further change.
The back of the camera should open outwards, on hinges, and be furnished with & thin flat board, on to which a piece of plate glass is cemented, to which the iodised paper is made to adhere just previous to being made sensitive) by wetting the surface of the glass and damping the back of the iodised paper; no glass need be placed in front of the prepared paper, nor do I think it will be found necessary to have any ground glass, as the focus of the lens can be obtained on the paper at once by looking through the small opening in front of the camera. There are several other minor details, which I cannot now enter into, but which I imagine a little experience will soon suggest.