When blisters have occurred, the paper at the back of each blister should be pierced with a fine needle, or, in the case of gelatine prints, and if the washing is finished, they should be placed in a bath of equal volumes of water and denatured alcohol, finally soaking in pure denatured alcohol (Eastman Laboratories, 5922).
Sticking of Gelatine Prints to Glass or Ferro type Plates. The glass or ferrotype slabs were not properly cleaned, or the gelatine was exces sively swollen when putting prints on the plates (insufficient tanning, washing in water which is too warm), or the prints (on the plates) were dried at too high a temperature.
Matt Patches on Glazed Prints. These patches, small and circular, or large with irregular out lines, are due to bubbles of air which were not expelled when laying down the prints, and thus have prevented contact between the gelatine and the polished surface. When glazing on plate-glass, these air bubbles are easily visible through the back of the glass, as they form patches which are more glossy than the parts where there is perfect contact. If the print is examined in this way, after it has been put on, such bubbles can be easily expelled at the time, or the print applied afresh after re-wetting it.
Gradual Deterioration of Prints. A slow deterioration of prints may be due to bad fixa tion or insufficient washing. In the two follow ing paragraphs the nature of such changes on print-out papers and on development papers is considered. In addition to these causes, change in the image may be due to impurities in the mounts and in the mountants themselves (the presence of hypo in the pulp of the mount ; acid glues to which hygroscopic materials have been added).
6i8. Failures with Print-out Papers. Bronzing of the Shadows. The formation of a reddish brown or metallic film on the dense parts of a print on print-out paper (particularly on col lodion papers or papers very rich in silver) is usually due to printing from a very contrasty negative and attempting to obtain details in the high lights, the shadows being considerably over-exposed. 1 If the metalliza tion is not very pronounced, it often disappears during toning and fixation, especially when the treatment used brings about a marked weaken ing of the image (this does not occur with self toning papers which have been treated with a salt bath). Bronzing can be remedied either
before or after toning. In the first case, after a brief washing, the prints are bathed in a very dilute solution of hydrochloric acid or a weak solution of gold chloride (II- drm. to I oz. of per cent solution per 20 oz. (10 to 50 c.c. per litre) ) to which a little hydrochloric acid has been added to 5i drm. per 20 oz. (5 to 35 c.c. per litre) ), according to the degree of the bronz ing. After washing for about io minutes the prints are toned, preferably with a combined toning and fixing bath containing ammoniuni sulphocyanide. In the second case, the toned prints are reduced by immersion for !- ore time in a fairly concentrated solution of copper sulphate (from io to 30 per cent), briefly rinsed, and transferred to the fixing bath. The metallic bronze on a print is often reduced by treating the surface with a wax or paraffin polish (A. Steigmann, 1925).
The Image as a Whole Refuses to Tone. This occurs only with separate toning baths, when the gold is exhausted, or when various impurities (hypo, sulphite, etc.) have gained access.
Parts of the Image Refuse to Tone. The parts which refuse to tone are not wetted by the solution owing to the presence of greasy spots (irregularly-shaped marks due to finger-marks) or circular spots due to air bubbles.
Brown or Black Stains. Local formation of silver sulphide by contact with traces of hypo from the fingers or a badly-washed dish. It should be a working rule not to begin fixation until a batch of prints has been toned, so as to avoid having to dip the fingers alternately into the toning and fixing baths.
Patchy Tones on Prints. The prints have adhered to each other during the toning (always keep the prints moving in the bath), or, when toning and fixing in separate baths, the prints have not been washed (or insufficiently washed) before toning.
Reddish Prints on Self-toning Papers. Too long washing before fixing. Self-toning papers should not usually be washed before fixing (or before treatment with salt solution), as washing removes the necessary toning materials (the directions given with the paper used should be followed).