Harsh prints are due to harsh negatives. They can generally be remedied by paying attention to the mode of printing, as given in [Chapter IX.] If the negative be under-exposed and wanting in detail, there is, however, no cure for this defect.
A red tone is due to insufficient toning; whilst a poor and blue tone is due to an excess of toning.
The whites may appear yellow from imperfect washing, imperfect toning, imperfect fixing, or from the use of old sensitized paper.
Should prints refuse to tone, either the gold has been exhausted, or else a trace of sodium hyposulphite has been carried into the toning bath by the fingers or other means. A trace of hyposulphite is much more injurious to the print than a fair quantity of it. Should the toning bath refuse to tone after the addition of gold, it may be presumed that it is contaminated by a trace of sodium hyposulphite.
A dark mottled appearance in the body of the paper indicates imperfect fixing, combined with the action of light on the unaltered chloride during fixing. If the fixing bath be acid, the excess of acid combines with the sulphur, and forms hydrosulphuric acid, which will also cause the defect.
The cause of mealiness or "measles" in the print has been explained in [page 32.]
[CHAPTER XXIV.]
ENCAUSTIC PASTE.
The value of an encaustic paste in improving the effect of photographic prints has become very generally recognised amongst photographers. A good encaustic confers three special benefits on the print: it gives depth, richness, and transparency to the shadows; it renders apparent delicate detail in the lights which would otherwise remain imperceptible; and it aids in protecting the surface, and so tends to permanency. One of the writers has in his possession prints that were treated with an encaustic paste thirteen years ago, which retain all their original freshness and purity, while prints done at the same time from the same negatives have gone, to say the least of it, "off colour."
Various formulæ for the preparation of encaustic pastes have been published, and many of them very excellent. The qualities required are, easiness of application, and the capacity of giving richness and depth without too much gloss, and of yielding a hard, firm, permanent surface. For a proper combination of all these qualities, nothing has ever approached the paste of the late Adam-Salomon, of which the following is the formula:—