It sometimes occurs, especially in cold weather, that when the prints are taken from the hypo and placed in the wash water, blisters form, spoiling the result. One cause for these is a considerable difference in temperature between the hypo and the water. This may be remedied by keeping the hypo at the temperature of the wash water. Another possible cause Is the use of too strong hypo. The easiest way to remedy this is to use hypo of a strength of not more than one to four. If a batch of prints shows these blisters, it may be put back in the hypo, when the blisters will probably disappear. If then a batch of hypo of half the strength of that used to fix the prints is prepared, and they are first changed to this and after a few minutes transferred to the water, they may be saved. The diffusion of the strong hypo solution does not take place so rapidly when this is done, and the blisters will not form.
A mistake which is often made by users of gaslight papers, is employing too contrasty brands of paper. The soft-working kinds are preferable for almost all negatives, and give much more harmonious prints. The so-called carbon brands, which give prints of great contrast, are not suitable for general use. Their special utility is the making of passable prints from negatives which are too thin to be printed on the special papers.