Magazine article Journal of Film Preservation

The Color-Restoration of Faded Color Film Prints

Magazine article Journal of Film Preservation

The Color-Restoration of Faded Color Film Prints

Article excerpt

The widespread and rapid fading of coupled developed color images has led to grave concern from those involved with the conservation of photographic resources. For a long time, experts in the fields of manufacturing, production and conservation of film have been searching for an effective means to improve the stability of color images. Film manufacturers have concentrated on modifying the nature of the color coupling and developing agents in order to reduce the rate of color fading, while film preservation specialists have focused on the improvements in the storage environment in order to extend the effective life of film resources. Also, a number of remedial processes have been developed to address this problem. In cases of moderate fading, color retiming, or a process for three color separation (with contrast adjustment made in each of the three individual color records) and recombination has been successfully employed. In the late 1970s, Kodak developed a duplicate mask technology to restore faded color images.

Nevertheless, all of these methods of color restoration are based on complex technology, and are slow and costly. Beginning in the mid- 1970s, we worked out alternate methods for restoring color film.This method is a chemical treatment which directly and selectively intensifies the color in faded negative, which allows the restoration of original color balance. This method of color restoration had produced good results, and is characterized by high speed, very low cost, safety and reliability.

1. The Process of Color Restoration

The characteristic fading of color film that has been stored in darkness is mainly hydrolytic reductive fading. Reductive decomposition takes place when the cyan, magenta and yellow colors in the coupling-developed image are subjected to attack from hydrogen ions (H+), hydoxy ions (OH- ), acidic sulfite ions (HSO3-) and thiosulfate ion (S2O32-) etc. Also, a further reaction turns the dyes into leuco-compounds.

The chemical products which are the result of the decomposition of the color-coupled dyes remain in the emulsion layer along with the remaining dyes, if the gelatin base has not degraded and dissolved. This provides the physical base for the process of restoration.

It is understood that during the development process of color-coupled film, the developer is oxidized into quinone-diimine cation, which combines with a coupler which has been dissociated into an anion, to form a dye. If we can introduce an oxidation agent which can oxidize the developer from the decomposition of dye into the quinone-diimine cation, and let the coupler form an anion with the aid of the developing bath, then we have already theoretically accomplished the restoration of the faded color image. Take the ferrocyanide anion as an example. It reacts with the color developer paraphenyline diamine as follows:

In this reaction, the developer paraphenyline diamine is oxidized into the equinone-diimine cation. In alkaline an developing bath, the coupler gains an electron from the hydroxyl radical and forms a coupler anion, as follows:

The quinone-diimine cation combines with the coupler anion to form coupling developed dye, and the lost color has thus been restored.

2. Oxidation-development dual-bath chemical color-restoration process

From these assumption, we began in 1976 to study the chemical restoration of faded images with faded film copies on Agfa, ORWO, Geva and color films stocks from the former Soviet Union of the type identified as water-soluble color positive cine-film. First, the faded film print is immersed in a solution of potassium ferrocyanide and other compounds to effect the oxidation treatment, following which the film is subjected to a color-developing bath. The results of experiments on scores of films demonstrate that all of the prints subjected to this treatment have show that almost all have been successful.

From table 1 and photograph 1, one can easily observe the distinguishing features of the oxydation-development process:

(1) Through this treatment, density of the yellow, cyan and magenta layers is substantially increased, by increments of 83. …

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