Glue, Time, Humidity and Heat: Mastering the Elements of Tape Preservation

This article has been reposted from the New York City Municipal Archives’ blog For the Record.

Typically, when preserving something in an archive one considers a time period of 100 years, if not longer. For example, the New York City Municipal Archives still holds records of the Dutch colonial settlement in New Amsterdam that date from the 17th century.  Thanks to the work of dozens of skilled archivists and conservators over decades, these documents have been and will continue to be preserved and made available to the public.

Unfortunately, the same cannot be said for the Archives’ video tape collections. It is likely that every tape in the collection will become unusable within the next 20-30 years. While video tape offered a lot of advantages over film as a recording medium, tape is one of the worst types of storage media. In this blog post, we will address what makes tape such a bad storage medium and what technicians at the Municipal Archives are doing to preserve the tapes before they are lost forever.

The diagram below illustrates how video (and audio) tape consists of three layers. Starting on the bottom is the back coat that shields the main structure of the tape from mechanical damage as it moves through the equipment. In the middle is the substrate, which is essentially a long ribbon usually made of polyethylene terephthalate (PET), a polyester film like Mylar, giving it a high-tensile strength.  The top coat is where all information is recorded. The Top Coat is the most complex part of a video tape and also where the most degradation happens.

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The top coat is composed of magnetic particles, lubricant reservoirs and binder. The magnetic particles are aligned by the video head when writing the video signal onto the tape, while the lubricant reservoirs help the tape move through the playback device, like a VCR. The binder is the glue that holds the magnetic particles and lubricant reservoirs in place, ensuring reliable playback and a consistent image. This binder is what is called the ‘inherent vice’ of all tape formats. Every other part of the tape is chemically stable and can last for hundreds of years, but the binder layer will fail, typically within a few decades.

In order to preserve tapes in the Municipal Archives, we need to keep three things in mind: time, humidity and heat. Over time, when exposed to enough humidity and heat, the binder layer will start to break down. The glue will absorb humidity from the air and expand as it gets warmer, losing its adhesive quality. As that happens, the magnetic particles will loosen, resulting in white pops or lines in the image quality. This binder degradation is called “sticky-shed syndrome.”

The optimal environmental storage conditions for video tape are 30-40% Relative Humidity and 40-50 degrees Fahrenheit. There is some wiggle room as most manufacturers changed their formula repeatedly, but keeping the tapes in a low humidity environment somewhat above freezing is crucial. Freezing video tape can cause the lubricant reservoirs to crystallize and fracture, shifting the magnetic particles within the binder layer. The PET ribbon might remain, but none of the binder will survive along with it.

Although all tapes regardless of their storage conditions will eventually develop sticky-shed syndrome, there is something that can be done to revive them: baking. By exposing the tapes to a low heat of 125 degrees Fahrenheit for 24-48 hours in a dry environment, binder that has begun to degrade can be stabilized. The Municipal Archives has rehabilitated a large number of tapes by baking them in a simple food dehydrator.

Here is a tape captured both before and after baking. Recorded in the East Village around the end of 1985, this tape has several segments of video suffering from sticky-shed syndrome. Below are three parts of the video tape with side-by-side comparisons of ‘before’ on the left and ‘after’ on the right.

This tape depicts the intensifying struggle for the rights of New Yorkers regardless of their sexual orientation.  On March 20, 1986, the New York City Council passed a law disallowing discrimination based on sexual orientation and the historically important content on this tape would have been lost forever if it were it not for baking.

So far, nearly 1,000 tapes from the WNYC-TV collection have successfully been digitized. Other videotapes that will be digitized include the Channel L collection of more than 1,700 items that depict city government officials directly engaging with residents of New York. Baking and digitizing these tapes will ensure that their content remains accessible for generations to come.