Russian scientists have discovered a method to prevent the deterioration of ancient film negatives.

The results of the study, supported by a grant from the Russian Science Foundation (RSF), have been published in the journal Heritage.

Nitrate-based negatives represent a broad class of photographic materials that emerged in the late 19th and early 20th centuries. Nitrocellulose as a material necessitates specific storage conditions: temperature, relative humidity, and lighting. Failure to maintain optimal conditions leads to the development of local, and eventually extensive, degradation (destruction), which threatens the loss of the negative and the image captured on it. Therefore, museum professionals must monitor and promptly identify the initial stages of degradation. This is often challenging due to the fact that the image on the negative contains a large number of details with varying shades.

Currently, there are laboratory methods—such as vibrational spectroscopy techniques—that allow for the precise detection of degradation at early stages. However, applying such approaches to a range of photographic materials, including negatives, is a labor-intensive process that requires specific laboratory equipment. Consequently, researchers are seeking a simpler express method to assess the degree of degradation of nitrate-based negatives.

Experts from The State Museum and Exhibition Center ROSPHOTO (St. Petersburg) proposed a pixel-based method for quickly assessing the preservation of photographic negatives. This method enables the identification of yellowed areas that indicate the initial degree of degradation of the nitrocellulose material.

For the study, the authors selected 40 photo negatives from the archives of the State Museum and Exhibition Center ROSPHOTO, taken by military veterinarian Karl Kossé between 1902 and 1917. Of these, 20 were in good condition, while the other 20 displayed clear signs of degradation affecting at least 75% of the image area. The degree of preservation and degradation was assessed using light scattering spectroscopy and infrared spectroscopy techniques.

In the next phase, the specialists examined the relationship between the preservation of negatives and the RGB component values (short for Red, Green, Blue) for individual pixels of the digital images captured from the examined negatives.

It turned out that the yellowed areas and well-preserved areas statistically differed in their blue component values. This distinction was observed for both dark and light tones in the images of the negatives. Based on this, the authors proposed formal criteria for separating preserved areas, borderline areas, and areas exhibiting signs of degradation. Identifying degraded (yellowed) areas is crucial to determine which zones require special attention during subsequent restoration. Additionally, monitoring changes in the area of individual zones will allow for timely identification of areas undergoing transitional processes.

The effectiveness of this new approach was demonstrated by analyzing an unevenly yellowed stereonegative, where the right and left sides represented similar images. The application of the new method allowed for the identification of stable, borderline, and degraded areas of the image.

“Detecting destructive changes in photo negatives at early stages is essential to timely and adequately implement restoration and conservation measures, thus preventing the complete loss of photographic museum exhibits. The proposed approach allows for quick and reasonably accurate assessments. In the future, we will attempt to apply the method to photo negatives with different polymer bases and integrate it with labor-intensive laboratory methods,” says Anastasia Povolotskaya, the project leader supported by the RSF grant, PhD in Physics and Mathematics, head of the Laboratory and Restoration Research Department at the State Museum and Exhibition Center ROSPHOTO.