Before polyester film became readily available in the 1950’s, all flexible film negatives were made on some form of cellulose nitrate or cellulose acetate support. Both of these film bases have deterioration issues, and in the case of nitrate negatives, health and safety issues as well.
Both nitrate and acetate film deteriorate, and
while some of the characteristics of their early deterioration are similar, distinguishing between the two and separating them is extremely important because the characteristics of their advanced deterioration are quite different. Chemicals released by deteriorating nitrate negatives can aggressively attack nearby negatives, prints, and housings and may turn recoverable acetate negatives into a negatives that cannot be recovered (more to come on the conservation of acetate negatives in Part Two of this post).
Sorting through off-gassing, actively deteriorating negatives to try to identify the film base and decide on a course of action for their preservation can be both difficult and unpleasant. While most of the negative collections that we work with have already been divided by media, some institutions prefer to defer to our expertise (and ventilation) when it comes to sorting through a collection of negatives with different bases and levels of deterioration which may or may not be salvageable for digitization/duplication.
Our routine for preserving the information from nitrate negatives at all stages of deterioration and from acetate negatives in the early stages of deterioration (without any bubbling, crystalline deposits, or channeling) is more or less the same. Before the prevalence of digital media, the standard practice for preserving information from deteriorating negatives was to create interpositives and duplicate negatives on archival polyester film. We now meet this preservation standard by creating high resolution scans and outputting to film via LVT film recorder which produces incredibly sharp, continuous tone, silver gelatin negatives suitable for either printing or as a preservation copy that can be scanned at a later date should the digital file be lost or corrupted. This allows for the best of both the digital and analog worlds, providing the accessibility of digital images and the durability of an archival hard copy. This is of particular importance for institutions or individuals with weak links in their digital migration strategy – a duplicate negative is human readable, unlike a digital file, and therefore does not need to be reformatted or migrated due to hardware or software changes. After this process has been completed, the institution or individual who owns the negatives may choose to dispose of the originals or place them into cold storage depending on their value as physical objects and the extent of their deterioration.
Our extensive experience with negatives is an advantage at every stage of this process. Assessing and working with many negative collections over the years has proven useful in being able to identify different film bases, even when they do not bare obvious characteristic traits. We are experienced in handling them and make every effort to carefully flatten curled nitrate negatives and separate them in cases of adhesion. In the case of broken negatives, the pieces may have shrunk at different rates and become deformed, making physically lining them up on the scanner an impossibility. In these cases, our clients have the option of having us digitally repair the image so that the cracks or breaks are not apparent.
The final stage of the process, making duplicate negatives, has been one of our specialties for over 30 years. We examine all film to check for both digital artifacts and analog flaws. All black and white film processing is performed in house where we regularly perform methylene blue tests to confirm that there is no residual chemistry, and every negative is checked for density, sharpness, and dust. For more information about our past clients and experience in this field, please see the history page on our website.
Resources for additional information on nitrate and acetate film deterioration, identification, and preservation:
Though this is published by the National Park Services and some of the recommendations are specific to NPS collections, this guide may be useful to other institutions faced with the sometimes daunting task of nitrate and acetate film identification and preservation:
Valverde, Maria Fernanda. “Guide for Identification and Preservation of Negative Collections.”: