The purpose of colour film restoration.
Restoring black and white film results in the production of a new print as much like the old as possible and the approach requires little decision making other than deciding what contrast or grading is needed to restore the original appearance. The resulting restored image is silver just as the original image was, and although modern materials do differ in response to older materials, in general there need be little difference between old images on old film stocks and new ones on new stocks.
Colour film requires more consideration as the dyes in use today in modern subtractive colour films are, in almost every case, different from those originally used, and in some cases modern subtractive dyes cannot be used to produce a match with some of the dyes used in the past [particularly the primaries of the various additive processes].
Almost all modern restoration techniques for archive colour film use modern film materials in a manner never used originally or ever intended by the film stock manufacturer. A good example is to consider the production today of a colour print from a set of three separation negatives made in 1940 for the production of a Technicolor print. The usual procedure is to print the separations onto black and white stock to produce a set of separation positives, print these in register through a set of tricolour [red, green and blue] filters onto Eastman Colour Intermediate Film and print this masked colour negative onto modern colour print stock. The result can be very good, but may bear little resemblance to a Technicolor print with its low resolution and narrow range of saturations. The print may be visually more like a modern negative-positive print than an original imbibition print. Using modern materials usually results in restorations that are a visual blend of characteristics of the old image and the new film material.
Since there is a choice of routes in many instances, it is necessary to establish what is the purpose of the restoration. The alternatives purposes are usually
A screening copy could be:
Sometimes a print made as it might have originally appeared is called a "simulation" of the original, and do this successfully usually requires a considerable knowledge of the original process.