If silver stain is treated as above, it will not be removed, but will be changed to metallic silver, and a black deposit will take the place of the yellow stain.

When a negative or print is stained, and it is decided to attempt its removal, it is a good plan to find out by a preliminary test just what particular variety of stain you have to deal with. This is done by cutting a narrow strip from the edge of the stained paper or film, and bleaching and redeveloping as described above. If the stain is removed entirely, it is pure oxidation stain, but if is replaced by a black deposit, it consists more or less of pure silver.

Artura Print, From An Eastman Portrait Film Negative By Moffett Studio Chicago, Ill.

Artura Print, From An Eastman Portrait Film Negative By Moffett Studio Chicago, Ill.

Whenever silver stain is present, it is a much safer and better plan to remove it photographically.

The following method of removing stains by means of color-sensitive plates and light filters was published in Studio Light, February, 1917.

"This special use we have in mind for a panchromatic plate and contrast-filter is for reproducing valuable negatives that have become so badly stained that they are useless for printing.

"Negatives become stained in various ways, and sometimes these stains cannot be removed by a chemical treatment without injuring the silver image. It is useless to try to print from them, but it is a very simple matter to reproduce them, provided the chemical that made the stain has not removed a portion of the silver image, and this is not often the case.

"A positive made by contact through the strong Wratten G' filter on a panchromatic plate will show no trace of the yellow stain. It is then a simple matter to make a negative on a Seed 23 plate from the positive, by contact, if the positive is of the desired size.

"Filter-film is not expensive, but care should be used in handling it. It is stained gelatine stripped from the glass-support on which it was coated, and without a support it must be kept absolutely dry to retain its form.

"On the other hand, an enlarged, reduced or full-sized positive may be made in the enlarging or reducing camera, in which case a piece of filter, only slightly larger than the diameter of the lens, will be required."

Apart from yellow stains, we may have brown iron-rust stains, or bluish stains caused by the action of pyroon such iron stains, though these are usually removed during the bleaching- and devel-oping-process above, as are likewise stains due to most aniline dyes, and red and black writing-inks. In the case of some samples of red ink, a slight trace of stain will remain after such treatment, in which case its effect may be removed photographically.

Although the previous article in Studio Light makes particular reference to the "G" filter for removing yellow stain, any colored stain may be dealt with in a similar manner by a suitable choice of filters, so that on viewing the stained negative or print through the filter, the stain becomes invisible.

Another form of stain, rarely met with, is dichroic fog, which appears yellowish green on looking at the surface of the film, but pink when looking through the negative. This stain consists of particles of colloidal silver, and is caused by underexposure and forced development of rapid plates or film with a developer containing hypo, ammonia or an excess of alkali or sulphite, that is, a solvent of silver bromide, or the use of a weak fixing-bath or one containing an excess of developer.

Anything which tends to increase the solubility of the silver bromide in the developer, such as an increase in temperature, tends to increase the amount of fog likewise. The stain may be removed by an application of a weak solution of Farmer's reducer, or a dilute solution of potassium permanganate with the addition of a few drops of sulphuric acid. This will be effective only if the stain is more readily attacked than the silver image, so that if the stain is of long standing, the slight reduction of the negative is apt to take place.

While oxidation stain is being removed by the above bleaching-and redeveloping-process, any drying-marks left on the film or plate, caused by too rapid drying, will disappear also.

Another advantage in the use of the bleaching- and redevelop-ing-method is that it affords an opportunity for intensification and reduction. If the negative from which we wish to remove stain is weak and thin, we can, in the redeveloping-stage of the stain-removing process, redevelop with a solution of sodium sulphide. If, on the other hand, the negative is too dense, by cutting down the time of redevelopment and subsequently fixing we can effect any degree of reduction. In this way we can make two improvements to our negative by the one operation, and if the negative happened to have any of the other stains mentioned above, we accomplish several improvements with one effort. The above methods of stain-removal may be applied to the removal of stains from sul-phided prints also.