The technique of pre-flashing duplicating or print film, giving a small overall exposure to white [or coloured light] by a separate pass through a printer, is also widely used to reduce contrast. Again this is simpler on black and white film, and permits greater variations than available from development control alone, but more difficult on colour. However pre-flashing colour stocks can be very successful especially if filtered exposures are used to effect one layer more than another, and thus correct for some induced "cross contrast" effects.
The procedures given below are to enable technicians to devise their own contrast control rather than describe a particular set of conditions with a specific film stock. It is inevitable that stocks used for duplication alter in specification from time to time, and are replaced by new films. Manufacturers of duplicating films do not devise them for archive use and a film archive technician must be familiar methods of adapting films for a non-standard purposes.
Pre-flashing is generally more effective in reducing contrast than post-flashing, which is frequently unpredictable and may add density rather than effect contrast.