The Tech Review: October, 2010

Film Preservation at the Library of Congress Packard Campus for Audio Visual Conservation
by Ken Weissman

Protecting our moving picture collection assets and preserving "America's Memory" for future generations is the primary goal of the film preservation program at the Library of Congress. The Library has operated an in-house film preservation laboratory for nearly four decades. Founded in the early 1970's, the lab was originally located in the basement of the Library's Jefferson building on Capitol Hill. The lab relocated to Wright-Patterson Air Force Base near Dayton, Ohio in 1981, taking advantage of the close proximity of nitrate film vaults that the Library had operated on WPAFB since the late 1960s. The film lab closed in April of 2007 as staff began relocating to the Packard Campus for Audio Visual Conservation in Culpeper, Virginia about 70 miles southwest of Washington DC.

Just a few of the doors
which lead to film vaults

The Library of Congress Packard Campus for Audio Visual Conservation has the primary curatorial responsibility for the Library's 6.3 million piece collection of audio, moving image, and film materials. Prior to the advent of the Packard Campus in 2007, the main focus of the film preservation program was the vast nitrate film collection, consisting of some 140 million feet of camera original negatives, original sound tracks, and projection prints dating back to the 1890s. With the new facility, the preservation focus has broadened to include all of the Library's film materials that are in need of preservation.

Because of nitrate's nature to eventually deteriorate (sometimes in rather spectacular fashion), the content on all of the thousands of films in the Library's collection is at risk. But so are films that were made of cellulose triacetate, as anyone who has un-spooled a film suffering from "vinegar syndrome" can tell you.

The Technical Challenges of Operating an Archival Film Laboratory

As most of AMIA's membership is aware, cellulose nitrate is a flammable material, but it also happens to be a very high-quality and exceptionally clear plastic, making it ideal for projection. Film manufacturers struggled mightily to come up with a nonflammable substitute that could match the optical and physical performance of nitrate film. But until that new base was found, 35mm motion picture film was almost exclusively nitrate from the beginning of filmmaking. Nitrate film remained in circulation through the early 1950s in the US and as late as the early '60s in Eastern Europe, Russia and China. With the advent of cellulose triacetate, nitrate was phased out of use in the United States and Western Europe. Beginning in the 1960s film manufacturers in the US began manufacturing a limited number of emulsions on polyester base. As expertise with this inert product broadened, its use has been extended to many more film products, pushing triacetate-based materials into the minority in common laboratory applications. An archival preservation laboratory needs to be able to work with all three of these film types or even reels of film that combine these various bases. But this is just the beginning of the challenges that face a film laboratory specializing in the preservation and restoration of archival films.

The bulk of the nitrate-era films are black and white, so that has been our specialty. Chemical formulas have been tweaked from time to time, but the development process hasn't changed very much since it was invented.

B&W film developing is as much art as it is science, which means that the final look of the print on the screen can be intentionally altered at the processing stage. The amount of time the film is in the developer and the temperature of the developer can be adjusted to compensate for the fact that we don't always have the luxury of an original camera negative as the source material when working on a preservation project.

Likewise the "copying" of old films to new stocks is not as simple as it sounds. There are many factors that can impact the quality of the final result, with shrinkage in nitrate and triacetate films being one of the most notable. It is a fact of life that shrinkage is unavoidable as these films age, but why does shrinkage matter?

Stock makers perforate newly manufactured film to very rigid standards-accuracy is maintained literally to the ten-thousandth of an inch. Camera negative film perforations have a pitch (essentially the distance between them) of 0.1866" while print stocks are perforated to a pitch of 0.1870". The 4 ten-thousandths difference enables the two films to be contact printed around the radius of a printing head, keeping the films in close contact with one another so that the image is as sharp as possible. The negative film or shorter pitched stock is on the inside of the radius, while the print stock with the longer pitch is on the outside. The slightly greater distance between the perforations allows the two pieces of film to remain in close contact during the printing process.

It was common for original era nitrate or acetate negatives to show shrinkage shortly after they were shot and processed of as much as 0.5%. But as nitrate film continues to age (and acetate film to a somewhat lesser extent), shrinkage can become more pronounced. Excessive shrinkage results in a loss of resolution, jitter, and/or general image instability and degradation when printed on machines designed to print fresh negatives. When source materials reach this stage of shrinkage, specialized equipment must be employed to produce duplicates which are acceptable.

Other challenges are associated with the amount of damage the film was subjected to over time. If the only remaining source material for a subject is a positive print, such prints frequently have been damaged to a greater or lesser extent by poorly maintained projectors upon which they have been run. In dry regions, static electricity can attract dirt to the surface of prints or negatives, where it may be embedded in the emulsion as the film was wound back up. These problems and defects can print through to new materials. Various pieces of equipment have been designed to help overcome these and other problems, including automated film cleaning machines to remove as much dirt as possible and wet-gate or full immersion printers to eliminate some surface defects, such as base scratches.

The introduction of wet-gate printers and immersion printers created a sea change in the world of preservation. They allowed laboratories to make fairly pristine copies from films that were otherwise horribly scratched. This is done either by applying or by immersing the film in a liquid-perchloroethylene, the same fluid used in dry cleaning-to temporarily fill in the scratches. When we look at films that were preserved prior to the wet-gate era and compare them with preservation work done from the same negative using wet-gates or immersion printers, there is often a remarkable difference.

The Library's film preservation laboratory has an interesting and diverse set of printers which it can use to preserve films in its collections. These include continuous-contact and step-optical printers, as well as several film scanners for direct-to-digital work.

We have 2 BHP model 6127R continuous-contact full immersion printers, which are the workhorses of the film lab. The printers can be used for either 16mm or 35mm film and they can be run as full immersion or as dry printers, depending upon the project. In addition to the standard heads, we have a set of specially modified heads for handling shrinkage up to around 2.25% for 35mm film and over 1% for 16mm film. These printers run at varying speeds, from 60 feet per minute in wet-mode up to around 480 fpm in dry mode.

For films that have higher levels of shrinkage or exhibit other problems such as extreme brittleness, we can use one of our two step-optical printers: an Oxberry model 1500 or an ACME 105. The projector portion of the printers move the film one frame at a time, pause, and then the camera side of the printer re-photographs the picture onto the new film stock. These printers are much slower, running at up to 10 feet per minute at maximum speed.

For the Oxberry printer we have a selection of dry and wet-gates with matching sprocket sets that enable us to print just about every gauge of film within the Library's vast collections. These include 8mm, S-8mm, 9.5mm, 16mm, 22mm Edison Home Kinetoscope, 28mm and various types of 35mm. This printer also features a variable pitch cam which allows us to adjust for shrinkage of the original. Some of the gates also allow additional adjustments; we seldom come up against shrinkage levels that are too high for us to transport.

We recently acquired an Oxberry Cinescan 4K step-optical film scanner that can also utilize the same wet-gates and sprocket sets, allowing us to go straight to digital files when needed, especially for use in restoration projects.

Preservation versus Restoration

For the most part the work being done at the film preservation laboratory comes under the definition of preservation. That is, we make as faithful a copy of the film that we have in our collection as we can. Restoration is a much more involved process beginning with answering the question: What is the right version of a given film to restore? There can be several different negatives and, especially as you get back to the 40s and earlier, there are few notes to describe what changes were made or why.

For example, we did a restoration of "Mr. Smith Goes to Washington" in 2002, and we were able to identify six different versions of the film, from roughly 119 minutes to 132 minutes. So, which one should be your guide? In our case, we chose to restore to the longest version. Based on research, including newspaper reports from the time, we became convinced that this was the version screened at the original premiere.

There are other more technical questions where the answer is not so easy. For example, what should we do if a film negative appears to have been underdeveloped? Clearly, there's art involved, so we must make a qualitative judgment as to whether this was intentional or merely poor lab work. If necessary, we can essentially force-process the master positive and to a certain degree adjust the gamma to make it more "normal." But there are ethical decisions that have to be made: If this is the way it has always been seen even by the original audiences, what right do we have to change it?

Whenever we make decisions like this, we document our reasoning. I have no problem with people being critical of our approach. If someone were to provide evidence that we took the wrong approach, we can go back to the original and redo it with the new information-although, quite frankly, we don't get criticized very often, because our reasoning is usually pretty sound.

Paper Prints

We started as a photochemical laboratory and we are primarily one to this day. However it has only really been in the past half-dozen years or so that you could even begin a conversation that might convince "people-in-the-know" that preserving motion pictures might be done digitally. To test this approach we conducted a pilot digital project for a very special collection that we have in the Library of Congress: the paper print collection.

These paper prints exist because of an interpretation of the copyright law at the time that motion pictures were invented. That interpretation said that a motion picture film is simply a series of still photographs and therefore the still photographic copyright law applied. If you wanted to copyright a motion picture, you had to provide the Library of Congress two copies of the film, and they had to be on paper-not film. Thus a process was invented to literally create long strips of photographic paper, exactly the size of 35mm film stock. Contact prints from the original 35mm negatives onto those long strips of paper were then deposited with the Library.

There are over 3000 titles on paper within the paper print collection. These are some of the earliest films ever made, coming from the period of 1894-1915, the vast majority of which are from before 1912. Most of them are unique-no other copies of these films are known to exist. They represent the single largest collection of early motion pictures in the world and the Library is rightfully very proud of that collection.

The paper prints had been locked in a vault in the bowels of one of the library buildings until rediscovered by librarian Howard Walls in the late 30s. Today the paper itself is still stable, but for the most part, you can't see the images very easily except by looking directly at the paper. Over the years there have been several projects to re-photograph the paper images back to film.

One of the first was by Kemp Niver and his company, Renovare. Niver took these 35mm prints (and there are some that are actually a larger gauge than that) and re-photographed them using a clever device that he built, printing to 16mm film. We have used various models of these Niver printers, including one where we replaced the 16mm camera with a 35mm camera in order to print back to 35.

All of the processes have been interesting and to some degree they've all been successful. However, for a variety of reasons, some of the images are alternately soft, fuzzy or very shaky, and up until now there has been no way to accurately register the images. In fact, we've concluded that in many cases the images weren't very well registered on the paper in the first place.

With today's technology, the obvious solution is to scan the images and then take advantage of digital processing to stabilize them, correct positioning and so on. Our first scans of the paper prints were 2K x 2K, which theoretically should have been good enough, but in some follow-up testing and subsequent analysis of the imagery, we think it might be better to go to 4K x 4K. But that's what a pilot program is intended to do-to figure out exactly how to do the job right. To date we haven't gone into a production mode due to some equipment issues, but we hope to implement a production work flow in the not too distant future.

Conclusion

The Library of Congress has been in the film preservation business for a very long time. With the advent of the Packard Campus for Audio Visual Conservation, the film preservation program enjoys a new facility in which to conduct its ongoing efforts. There are also plans for expanding the program's capabilities, such as color film developing and film sound re-recording. The future is bright with promise, and it will be interesting and exciting to watch it unfold, with more information to be presented in this forum. Stay tuned!