THE PHOTOGRAPHIC NEWS. VOL. X. No. 399. April 27, 1866
FOR some years past we have received from time to time examples of a peculiar defect in albumenized prints, with inquiries as to the cause and cure. The spots have puzzled us, and we have not been able with any certainty to indicate their origin or to suggest a remedy. They consist in minute spots of a pale greenish-yellow, suggesting imperfect fixation. They have varied in size from a mere point to a disc the size of a pin's head. They are generally perfectly round, are sometimes alone, sometimes in clusters or groups; and when one is present, there are generally more on the same print; The minuteness and perfect roundness have forbid the notion of patches of imperfect fixation from the sticking together of the prints, &c.; and the only solution has been the probable presence of minute specks of foreign matter in the paper which produced the spots in question by its reaction on the hypo fixing bath. It has generally been observed that these spots have appeared whilst the prints were washing; sometimes they did not appear until the print was mounted, just as patches of imperfect fixation behave. These troublesome spots appeared, however, in the hands of the most careful printers, as well as in the hands of the most careless; some of the most eminent photographers of the day having been pestered with them, without being able in any way to account for their presence.
The common piece of injustice to which manufacturers of materials are inevitably subject of course occurred here. No possible cause in the manipulation or formulae being apparent, the manufacturers of paper were naturally blamed, and this the more naturally, seeing that certain samples of paper were more prone to this defect than others. We are glad to say, however, that another solution of the problem has come under our notice, which perfectly accounts for the phenomenon, and which, we have no doubt whatever, is the real explanation. We cannot verify it with certainty, because we have not, in our own practice, met this trouble for many years. The explanation, how ever, seems to coincide with all the facts. The spots really are caused by imperfect fixation, and their peculiarly regular shape and minute size is readily accounted for. They are caused by the formation of small air-bubbles on the print when it is first immersed in the fixing bath. These bubbles, which adhere very tenaciously, and are not removed always by the mere agitation of the print in the bath, protect the point upon which they are formed from the perfect action of the fixing solution. Sufficient effect is produced to form the insoluble hyposulphite of silver, which is left in the print, and decomposes either in the washing water, or after the card is mounted and exposed to light and air, forming greenish-yellow, or brownish-yellow spots. The cause being discovered, the remedy will be tolerably apparent. Wherever a sample of paper is met with which has the tendency to form these bubbles on contact with the hyposulphite solution--and thick Rive samples will be found most prone to this peculiarity--the bubbles must be carefully looked after and removed, and the spots will be avoided. We are indebted for the solution of this difficulty to a correspondent, to whose letter, in another column, we invite the attention of our readers.