BENNETT'S TONING BATH FOR P.O.P.
A combined toning and fixing bath that gives rich purple tones on most brands of P.O.P., introduced in 1908 by H. W. Bennett. It con tains a sufficiently large proportion of " hypo " to ensure perfect fixation of the prints, and the bath is rendered slightly alkaline with ammonia. Prints toned and fixed in this bath are as per manent as any silver prints ; they preserve their original richness and freshness unimpaired for many years. A feature of the bath is the fact that separate solutions are kept of each ingre dient, and they are so adjusted that equal quantities of each are taken, excepting the " hypo " solution, and r oz. of that is required for each drain of the others. No calculation is needed, whatever quantity of solution may be required. Five solutions are necessary :— A. Sodium hyposulphite . . r lb. Water, sufficient to make . 32 oz.
The " hypo " should be dissolved in boiling water.
B. Ammonium sulphocyanide . 2 oz. Water to make . . . 8} „ C. Lead acetate . . r „ Boiling water to make . 81- „ A dense precipitate will settle. The bottle must be well shaken each time any solution is required.
D. Gold chloride . . . x5 grs.
Water . . . 2 OZ. 7 drms.
E. Strong ammonia . . 120 mins.
Water to . . . . io oz.
Each solution will keep indefinitely. To pre pare the bath, mix together in the order given : oz. of A, i drm. of B, i drm. of C, 2 oz. water, drm. of D, and i drm. of E. The measure must be thoroughly rinsed after measuring C and D. The solution is ready for use in five minutes. This quantity is sufficient for ten quarter-plate prints ; a suitable quantity for any other number may be prepared by allow ing oz. of A for every five quarter-plate prints, and remembering that whatever number of ounces of A solution are taken, the same number of drams of each of the others will be required. The prints are immersed in the bath without previous washing, and they should be put in the solution one at a time, and each one thoroughly wetted before the next is added. All the prints that are to be toned in one dish should, however, be put into the solution as quickly as possible consistently with covering each with the solution evenly.
As soon as the last print is placed in the dish the first should be taken from the bottom, brought to the top, and quickly examined. Should any air-bells have formed on the surface they will show as dark marks ; but if they are broken at once with the finger they will not show on the finished print. The second print that was placed in the bath will now be the lowest ; this should be brought to the top, and so on with each print in turn, until all have been changed in position. Throughout the operation the same method of procedure must be followed—the lowest print brought to the top ; but after the first changing the work should proceed more leisurely, leaving each print a longer time at the top of the solution. The minimum time of immersion in the bath is twelve minutes in hot weather if the temperature of the solution is 7o° F. (21° C.) or more, and fifteen minutes in cool weather, though the toning should not be done in a room at a lower temperature than about 6o° P. (15.5° C.). This minimum time is very important ; if less time in the solution is given, imperfect fixing will result. Longer time may be allowed if cooler tones are desired ; twenty minutes will not be too long. If warmer tones are required, the composition of the bath must be varied, so that the desired tones are not reached before the prints are fixed. The amount of water used for making the B and C solutions may be increased to x r oz., and for the D solution 3f oz., and the bath still pre pared by taking x drm. of each for r oz. of A. As soon as the minimum time has elapsed, or the desired tone reached if longer than the minimum time, the prints are taken from the bath and at once well washed. If washed in water that is frequently changed, from one to two hours should be allowed, according to the frequency of the changes and the quantity of prints in one dish. Prints for this toning bath require to be very deep.