NOTES ON WASHING.
The finished prints must be entirely free from Hypo. To wash a batch of foo 4 x 5 prints, using tw o trays of suitable size and transferring each print separately from one tray to the other, changing the water at least twelve times, will take a full hour for the process. In running water w-here the prints can be kept constantly moving so that each individual print has a thorough washing, from one-half to one hour, according to the number of prints, will be required. Prints do not wash if piled in a bunch in a tray and the water simply runs in at one end of the tray and out of the other. In some localities where there is an excessive amount of iron or impurity in water, the whites in the prints may have a slight yellowish tone. Prints should not be allowed to wash for any len.i,-th of time over one hour and should never soak over night in water as this tends to soften the gelatine film and entirely spoil the print. The temperature of the water in winter should be kept as uniform as possible, as ice cold water will cause blistering.
When running water is used for m ashing, the stream should not be allowed to fall directly on the prints, as it will cause breaks in the fiber of the paper, producing blisters. Place a tumbler or graduate in the washing tray and allow the water to overflow from it into the tray, To determine w-hen the print is thoroughly free from hypo, the following test formula may be successfully employed.
Permanganate of Potash, - 8 gr.
Caustic Soda, 7 gr.
Water (distilled), - S ozs.
Fill a glass with pure water to which you have added 3 or 4 drops of the potash solution. Then take a couple of prints from the wash-water and allow the water from the prints to drip into the glass. If hypo is present, the violet color of the water in the glass will change to a slight greenish tint. In such case rcturn prints to the wash-water to remain until similar tests show- that the hypo has been entirely eliminated.