=Retouching Negatives and Plates.=—The negatives must have all defects made good by the retoucher, all blemishes being moderated as far as possible. Retouching on the Collotype plate or print should not be required; but this is seldom so, as during the printing the negatives frequently sustain slight damages. Retouching the printing surface is seldom very successful. The alteration easiest effected is the removal of small light spots which refuse to take the ink, and such may be removed by touching with a fine brush dipped in a strong aqueous solution of tannin, this alteration being made upon the finished plate after it has been washed and dried. With this tannin solution inscriptions may be inserted which have to appear black in the print. Or a solution of gum arabic, to which has been added a solution of bichromate of potassium, may be used, and after such addition the plate is once again exposed to light. Writing which has received too much exposure, and which should appear in the finished print black on a white or light ground, often appears white. This defect arises from the gelatine on which the light has had little or no action swelling to such an extent that the letters are buried or sunk into the plate too deep to be touched by the roller when the plate is inked. It may be rectified by further thinning the ink with varnish. The removal of dark spots from the print layer can never be completely effected. Ammonia, cyanide of potassium, oxalic and other acids have from time to time been recommended, but this treatment will prove effective for only a few impressions. Negatives should therefore be very carefully and systematically retouched and carefully preserved from damage during the printing. Another method of applying writing, such as the names of firms, &c., is to get them printed from small type on thin gelatine films and attach them to a clear or erased portion of the negative during the printing in the pressure frame. Writing so added will appear as white letters on a black ground. It will often be found practicable to attach the written or printed matter to the original while photographing, and so include it in the negative at one operation.