The retouching of a negative should always, if possible, be done before varnishing, such portions of the negative as are to be operated on being covered with a retouching medium. This medium may be purchased, or may be made of gum dammar 96 gr , turpentine 1 oz. If it is preferred to varnish before retouching, the varnished negative must be rubbed down with powdered resin to give a surface on which the retouching pencil can be used. The following varnish is recommended. Sandaiuch 1/2 oz., seed lac 3/4 oz., castor oil 80 drops, oil of lavender 40 drops, alcohol 10 oz. Powder the resins and dissolve in the alcohol, and add the rest of the ingredients. Warm the negative till it is as hot as can be comfortably borne by the back of the hand, pour a pool of varnish in the centre of the plate, ana let it flow first to the top right-hand corner, next to the top left-hand corner, then to bottom left-hand corner, almost touching the thumb, and pour off the excess at the bottom right-hand corner into the bottle. The negative should not be rocked. If the varnish is inclined to be streaky it is too thick, and more alcohol must be added. Conduct the whole operation as slowly as possible.

Drain thoroughly, and bake the varnished negative in front of the fire or over a gas jet till the varnish is quite hard. Heat the negative evenly or it will crack. The negative should be held by the extreme corner with the thumb and forefinger of the left hand, unless it is larger than half plate.