INTENSIFICATION WITHOUT BLACKENING.
A negative which has been bleached in mercury may be printed from, and gives an increase of density somewhere between the spirit method and the sulphite. With the silver intensifier, only one operation is necessary, the negative as suming correct density in the solution and simply requiring washing. The sole draw back to the process is that, besides being rather tedious, it is distinctly expensive. The following stock solution, known as Wellington's silver intensifier, will keep in definitely if stored in the dark : Silver nitrate ... GO grs.
Ammonium sulphoeyanide ... 120 grs.
Water (distilled) 2,1 oz.
Dissolve the silver nitrate in half the water. The sulphocyanide is then added, the mix ture well shaken, and the remaining water introduced. When required for use, the bottle is shaken and a sufficient quantity of the solution into a glass measure. The solution being rather costly, it should be used sparingly, only just enough being taken to cover the plate ; half an ounce will suffice for a half-plate if a flat dish is used. To the solution in the glass measure add gently, and by degrees, a freshly made hypo. solution, stirring con
stantly, until the milkiness at first present disappears and the liquid becomes clear. No more than sufficient hypo. to secure this result must be added. To each ounce of the mixture, 3 grs. of pyrogallie acid (pre viously dissolved or from a stock pyro. solution), 5 minims of ammonia (880°), and 1 gr. of ammonium bromide are added. The solution is then poured quickly over negative, which is allowed to remain until sufficiently dense, making allowance for the fact that it will be a good deal more opaque when dry. If the intensifier seems to act too slowly, a drop or two more of ammonia may be added. Do not, however, add so much as to cause the solution to turn muddy, or it will have to be thrown away. When the negative is sufficiently dense, it is placed in a dish of fresh hypo. for about a minute, 'and then washed thoroughly. If the film becomes tender an alum bath may be used after the plate has been washed for about ten minutes ; it is then given a final washing.