Making a mask.

In order to reduce the problems of “fringing” caused by a mask not being perfectly in register with the original image, masks are usually made slightly unsharp, and since contact printing is almost universal in order to make the image exactly the same size, the mask is usually exposed through the base of the original. Masks may be made on black and white or colour stock, negative or positive, depending on the purpose of the mask.

This procedure is extremely difficult on any printer, and is generally only done on a step contact printer. Printing on an optical printer is possible only if the printer has been specially designed for this. Rotary contact printers are also difficult although this is more commonly done in order to produce subtitles and the degree of slip and imprecision makes registration very imprecise.

An extra set of supply and take-up spools and a drive are needed to supply and rewind the mask, roll which will usually be the same length as the original roll.

Masks are usually used for two procedures:

To combine with an original during the printing of a separation negative or positive.

To combine with the original when printing a colour internegative or intermediate.