Photographic Reproduction Processes

CAUSES OF FAILURES.

The images are veiled.

This defect may result from various causes, viz.:

1st.	The stock ferric oxalate solution is impaired by a partial reduction of the ferric salt into ferrous oxalate. The solution should be preserved in an orange colored vial, and kept in the closet of the dark room. It should be tested from time to time for the ferrous salt with a solution of potassium ferricyanate. If it does not contain any ferrous oxalate it can be used by adding to it a little of the iron chlorate solution.
2d.	The paper has been exposed to light during the sensitizing or the subsequent operations. One should bear in mind that the platinum paper is twice more sensitive than silvered paper.
3d.	The sensitized paper has been dried at a temperature above 40 deg. C. (104. deg. Fahr.)
4th.	Over-exposure.

The proofs are not sharp.

1st.	The sensitive paper has absorbed moisture.
2d.	It is too old. The paper cannot be kept good for over six weeks, unless special care be taken.

According to Mr. Bory, the sensitive paper altered by keeping is restored to its original good quality by simply brushing it over with a solution of 0.05 parts of potassium chloride or the same quantity of potassium chlorate in 100 parts of distilled water, or a mixture of these two solutions, or one of iron chlorate.

By treating the insolated paper with these solutions, the image is destroyed, and the paper can be used again. One operates as for sensitizing, taking care to desiccate the paper, as it has been directed.

The proofs are brilliant during the development, but become dull in drying.

The paper not well sized. It has been dried too slowly.

[pg 80]

Remember that it should be quite desiccated within fifteen minutes.

The paper is more or less yellow.

1st.	The paper tinted with ultramarine.
2d.	The sensitizing solution or the developer are not sufficiently acid.
3d.	The washing (fixing) in the solution of hydrochloric acid was not sufficient to eliminate the iron salts from the paper.

The proofs harsh, devoid of half tones.

1st.	The sensitizing solution contains too much iron chlorate.
2d.	Exposure too short.

The paper is stained.

The brush not kept clean while sensitizing.

Black spots.

They are generally due to metallic dust in the paste of the paper, or from particles of undissolved salt in the platinite solution.

NB: No good results can be expected unless the paper be kept absolutely dry before, during and after exposure, when using the former (original) process.

Impaired sensitiveness of the paper, want of vigor, tinged whites, muddiness, indicate dampness.

[pg 81]

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