LONG TERM CONSERVATION.

If the purpose of restoration is primarily to preserve the image in a reliably permanent manner that allows later reconstruction and/or display, then the method most in use is to generate red, green, blue monochrome separation negatives or positives on a modern silver image material that are independent of the permanence of any dye images. Sometimes polyester base is used but most archives use modern acetate based film stocks. These separation images record the colour of images as they are today, after any fading that might have occurred.

If the elements available are already monochrome separations that need to be restored then high quality monochrome duplication as described in a previous chapter is required. Other systems have also been proposed to do this, such as the use of digital video signals, on disc or tape, but the permanence of a silver film image on a modern film base is still considered more certain than the unknown life of any video system hardware.

Many colour systems in the past included the use of black and white separations as "protection masters", sometimes called "PM's" or “Pro-Masters”, and these were particularly used by major film producers for storage. However, they are not a single consistent format or element and their contrasts depended on the originals from which they were made. PMs made from Technicolor separation camera negatives are positives of a high contrast [almost that of a conventional projection print] whereas PMs made from Eastman Colour Negatives [also positives] were of much lower contrast.

Once a set of PMs existed, a printing negative or negatives could be made from them at any time.

In the Technicolor process, the PMs were printed onto a black and white duplicating stock to make a colour separation negatives. From these the matrices used for the imbibition process could be produced.

PMs from an Eastman Colour Negative could be printed onto Eastman Colour Intermediate through tricolour red, green and blue filters in register to produce a duplicate colour negative. Once these two principle routes are established in a laboratory and set ups exist so that they can be performed repeatably, they constitute the basis of almost all colour separation restoration.