Platinotype

paper, solution, prints, drying, weak, kept and sensitizing

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Drying and drying the prints are dried in the ordinary way. Any mountant can be used that does not show through the print. Gelatine alone is not suitable except for thick paper. Thick cold starch, or starch and gelatine, are the best mountants.

Platinum prints appear somewhat more brilliant and lighter when wet than when dry; therefore, if it has a correct appearance as regards tone when wet, it will be too dark when finished. Prints on smooth paper may be hot-pressed, which gives them a slight sheen, and brings up the dark parts. They may also be retouched with colors or chalk, their smooth, heavy surface serving well for this purpose.

The following list of defects and their remedies is given by Captain Pizzighelli and Baron Htibl : i.—The pictures are vigorous, but more or less fogged.

(A) cause: The paper was affected by light either in sensitizing or printing.

To prevent it sensitize only under a weak light, and dry either in complete darkness or by lamplight. When examining the course of the copying operation be careful to avoid too strong a light in arranging the frame.

(B) cause : Too high a temperature in drying..

It should never exceed 4o deg. C.

(C) cause : Spoiled ferric solution.

The ferric solution is best preserved from the influence of light by being kept in a hyalite flask. If you are not confident as to your solution, you must assure yourself before using it by testing with red prussiate of potash that it is free from ferrite. Should it only contain a trace of ferrite it can be made fit for use again by carefully adding red prussiate of potash. In order to try this, mix a few cubic centimetres of the normal ferric chlorate solution with every zoo cubic centimetres of the iron solution, and ascertain by actual experiment on paper whether the restora tion is complete.

(D) cause : Too long exposure in the printing frame.

The time of copying should be shortened, and if the picture is not yet developed use a cold developer.

2.—The prints appear too weak under the developer.

(A) cause: Paper which has become damp.

The paper should always be kept in the calcium chloride boxes, even after being printed, if not immediately developed. Paper once spoiled cannot be made good again.

(B) cause : The paper is too old.

Paper can generally be kept in good condition for, at least, six or eight weeks, and some times even more; but after that time even a gradual change appears to take place, even though it be kept in the dark, and not only weak, but also fogged pictures are the result. As neither time nor trouble are required for sensitizing the paper, we recommend only to make at once as much as may be necessary for use during three or four weeks.

(C) cause: Weak negatives.

Use more chlorate of potash in the sensitizing solution.

3.—The prints come out vigorous in developing, but become weak after being dried. Paper not sufficiently sized, for which reason the image sinks into its substance. When this is the case employ stronger solutions of gelatine or arrowroot.

(A) cause : Drying has been too slow.

The drying process should not take longer than ten minutes ; if this is exceeded the sensi tizing solution sinks too deeply into the paper.

whites of the prints have, after drying, a more or less yellowish tinge.

(A) cause: The sensitizing solution in the developer is not sufficiently acid. Attention should be paid. to the instructions on this point in the previous divisions of the subject.

(B) cause: Insufficient immersion in hydrochloric acid.

The solution of hydrochloric acid must be changed two or three times,, until the last change no longer turns yellow at the end of ten minutes.

(C) cause : Paper blued with ultramarine, which, when treated with hydrochloric, turns yellow.

Before using the paper you must be certain that its color does not suffer from contact with a hot solution of oxalate, and from treatment with hydrochloric acid.

5.—The prints come out hard.

(A) cause : Exposure too short.

(B) cause: Too much in the sensitizing solution. Remedy obvious.

6.—Spots and streaks.

Causes: Dirty brushes; touching the paper with wet fingers; dirty glass plates; vessels not kept clean, etc.

7.—Black spots.

(A) cause: Particles of metal embedded in the substance of the paper, causing a reduction of the platinum.

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