Issues affecting scanning old negatives

1 Reproducing the original print

There is considerable interest today in scanning old negatives. It provides a way to make interesting old pictures often of considerable historical value, more easily accessible to a wide audience. It's also a way to preserve them because once scanned the often fragile negatives don't need to be handled .

Yet scanning these negatives is not the same as scanning today's produced as they are by carefully standardised and controlled processes. Before the days of either accurate light illumination or light metering it was impossible to control the density of the negative other than by experience and having several tries. A much larger amount of correction was therefore undertaken at the print stage. Its this that has to be reintroduced in scanning these negatives today.

Imagine a scene of a brightly lit subject's face against a black background. Today the negative will be exposed for the face but clear for the black background. At the turn of the (last) century the background would almost certainly be a light to mid grey with detail from the different lighting levels clearly showing. According to accepted scanning rules all the detail in the background should be faithfully reproduced giving a flat low contrast picture of the subject. What has to be done rather is to clip the scan - as the photographer would have when printing - so that all the extraneous background is removed. Of course because of the judgement element in this on occasion there may be several alternative interpretations of what the original prints would have been like. These are all the factors that the original photographer had at his disposal when printing - harder or softer papers, the degree of exposure, burning or dodging, staining and tinting and so on.

2 Handling the negatives

Film can be damaged easily, even when in good condition. It can be scratched, abraded, and creased. Oils and dirt from hands can also damage either the film base or emulsion.

If the film base has begun to deteriorate it becomes even more prone to handling damage. Deteriorated materials can become quite brittle. In this state, repeated removal from a housing can cause considerable harm. Furthermore, deteriorated materials may become sticky and adhere to other materials.

3 Preventing Deterioration

It's the film base material that is the primary concern once handling is controlled. There are three main types: Cellulose Nitrate, various types of Cellulose Acetate, and Polyester. Unfortunately, Cellulose Nitrate and Cellulose Acetate are unstable. Their degradation products can severely harm and even destroy photographic collections, in addition to posing health and safety hazards. Cellulose Nitrate is extremely flammable, especially when in a deteriorated condition.

The many fires caused by Cellulose Nitrate film lead to the development of Cellulose Acetate film during the 1920's, which.even when deteriorated does not have the flammable character of Cellulose Nitrate and it became known as "Safety" film. However, the Cellulose Acetates do have stability problems. Like Cellulose Nitrate, the deterioration of Cellulose Acetate is auto-catalytic - once deterioration has begun the degradation products cause further deterioration. Because of its increased stability, Polyester has replaced some Cellulose Acetates since its introduction in the 50's but Cellulose Acetate is still used as it can be solvent welded.

Maintenance of a proper environment is extremely important to the longevity of all films. Deterioration is heavily dependent on both temperature and relative humidity. Present recommendations are for a constant cool dry environment with a temperature of 5°C and 25% relative humidity being ideal if rather cold for viewing. The Image Permanence Institute at Rochester Institute of Technology can provide further data

Ideally, Cellulose Nitrate material should be stored separately, isolated from other types of film but this is often impractical due to the difficulty of identifying the base material. The advantage of doing this is that the nitric acid formed by its degradation can fade silver images, cause gelatin binders to become soft or even tacky, and corrode metal containers. The fire hazards associated with Cellulose Nitrate negatives may make special storage a condition of insurance.

It is also important to segregate deteriorating materials from those in good condition. As mentioned earlier, deteriorating materials produce degradation products that can induce deterioration in other photographic materials.

Sleeves should be made of unbuffered acid free, high alpha Cellulose content paper. Ideally it should be seamless and have no adhesive, although a side seam may be acceptable. As it,s porous it allows the degradation products to escape, unlike plastic which traps those harmful products and accelerates deterioration. If the films are used frequently, an optically transparent plastic sleeve may be desirable to reduce handling.

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