This Film is Dangerous: A Celebration of Nitrate Film

Bigourdon, Jean Louis. "From the Nitrate Experience to New Film Preservation Strategies." This Film is Dangerous: A Celebration of Nitrate Film, ed. Roger Smither. Bruxelles: Federation Internationale des Archives du Film (FIAF), 2002. Pages 52-73.

Here are some notes from the chapter of this really collection of essays on film called This Film is Dangerous. Let's start out with the basics.

There are three components of all types of photographic film: the support (or base), the image (or emulsion), and the binder (which holds the other two together). The support moved from a cellulose nitrate backing to a cellulose triacetate backing to a polyester backing. The image layer relies on one of two types of materials: metallic silver particles [think glitter] for black & white images; and color dyes for color film. The binder is almost always gelatin. (Which might be why Cosby and Jello make so much sense together. ;-)

According to Bigourdon, it was only in the late 1880s that it became possible to manufacture a "sufficient length of film" to make a motion picture of substantial length--i.e. a long enough roll of film to hold all of the image frames on. In 1889, Eastman Kodak started to develop film on a cellulose nitrate plastic backing. He talks about the properties of nitrate film base, and the challenges of preserving inherently unstable chemical materials (really active compared to paper). He notes that "any kind of film is subject to spontaneous chemical decay." Later acetate film bases had their own problems, and symptoms of decay include: vinegar syndrome (the smell), and color fading. That film is also likely to become brittle. Cellulose triacetate base was phased in gradually and came into full usage by the 1950s (about the time that nitrate film stopped being used for new film stock). Polyester film came along in the 1960s, but wasn't fully adopted until the 1990s. Indeed, camera original film is still acetate in base.

Nitrate and acetate aren't that different. Both are developed by a similar process, that of esterification. The forming of nitrate base involves nitration, and acetate base involves acetylation. The latter is a mixture of acetic acid, acetic anhyride, and a catalyst like sulfuric acide. Three acids in one! In both cases the polymer and solvents combine to form those types of film. Earlier ways of acidifying film involved using cellulose diacetate (which is prone to shrinkage), acetate propionate, and acetate butyrate). Oy--if I had only taken a chemistry course in the last 10 years!!!

1955 brought the advent of PET, or polyester polyethylene terephthalate. Polyester for short, which was made by adding solvent and plasticizers to the polymer.

Back to nitrate...so, nitrate is basically modified cellulose. It's highly flammable, unlike acetate which burns slower. In the 1930s, some of the dangers of nitrate film came to be understood, and manufacturers and those in the film industry responded by coming up with useful handling procedures, proper transportation and use regulations, better ways to construct vaults, and better can and cabinet design. Most of which was done to prevent fires, and their spread.

What happens to nitrate film after a certain number of years? Well, there's 5 stages--which I'll get into in a future post. But like other organic materials, the nitrification of film base can happen because of heat, oxygen (oxidation), acid, and moisture (hydrolysis). The moisture can act as a reactant which releases acids from the nitrate. It can become brittle and decompose. There can be amber discoloration, degradation of the binder, softening/[melting?] of the emulsion, strong odors, and eventually it might decompose into a pile of brownish powder.

The emulsion is at risk when the base degrades, because of certain reactions with the silver or the dyes. Silver corrodes when exposed to oxygen. Dyes can fade in light. The silver on acetate film doesn't decompose as quickly or harshly as on nitrate film. Why? Bigourdon says that when nitrate degrades it produces oxidizing compounds that oxidize the silver. And when it's hydrolized, the resulting nitric acid decomposes the gelatin binder. Oy.

So, in the 1930s, it became recognized that film was not only a vehicle for ephemeral entertainment ventures, but could be important cultural records in themselves. Their preservation efforts were focused on dealing with the flammability of these materials, constructing better storage spaces and enclosures, and providing "cool storage" for these materials (15 degrees C, 60-70% RH!!!), and doing experiments in film base stability.

Jump to 1948 when cellulose triacetate was the film base of choice. Why was it advocated? It burned slower, and as such was considered safer for handling and exhibition. But itself was a preservation problem. Acetate film, according to Bigourdon, is an unstable plastic, and like lacquer discs, can delaminate; and be susceptible to vinegar syndrome and all the wonderful things that happen to materials with acidic material in them.

So, how does one deal with these materials. According to this chapter, three strategies should be employed: 1) environmental control, 2) a condition assessment, and 3) a prioritized duplication program.

You can detect acidity with Acide Detector strips for nitrate based film, and A/D strips for acetate based film. For the silver emulsion, there's the alizan red test method. And Kodak has a way to test for color dye stability as well. You can find some of this stuff in two publications by James M. Reilly: IPI Storage Guide for Acetate Film and the Storage Guide for Photographic Color Materials. Cold storage can prevent dye fading, and slow down other chemical reactions.

This book contains some wonderful photographs, tables, charts and graphs relating to reaction times, timelines, etc. Much of what Bigourdon talks about with catalyzation and chemical reaction, I knew from Jake's class last semester. So, this reading was more about the physical nature of film--which I'll be reading for next week.