Special problems for video  tapes

Magnetic Media DiagramVHS Tape path TOP: Typical video tape construction. BOTTOM: Typical VHS Tape path, courtesy howstuffworks.com

Video tapes have a large and special set of longevity problems, apart from traditional chromogenic photos. And while their imaging clarity was never as good as most photographs to begin with, these memories, often home videos, need to be protected, too.

Anatomy of a video tape

Video tapes--the VHS, SVHS, VHS-C, and Hi 8 that most of us have been using for years--are fundamentally composed of three layers: the binder layer, the substrate, and the backing. While there are many differences from manufacturer to manufacturer, the engineering of these layers is a result of a very special need that video tapes have that photos don't, which is to survive the friction and stress of repeated playback, winding, and re-winding.

The binder layer comes into direct contact with the heads of the playback machine, and is responsible for signal quality. It contains magnetic particles (sometimes referred to, a bit anachronistically, as pigments, even though they are usually iron oxide) that store information on the tape. They are usually suspended in the binder along with lubricant, whose purpose is to seep out during playback, microscopically speaking, and prevent damage to the binder layer by the drum and head of the playback machine.
The substrate and backing layers are there for dimensional stability and strength, since the binder layer itself is quite thin. The backing in particular also helps with reducing friction.

How VHS and other magnetic tapes degrade

Example of Delaminated Video TapeAn example of a completely delaminated video tape. The binder layer (brown) has separated from the backing. Source: Anothermelbournite

VHS, VHS-C, SVHS, Hi 8, Digital 8, and even DV all share one thing in common: they are magnetic media. And the trouble with magnetic charge ("remanence") is that it is fundamentally impermanent. But that's just the beginning of the trouble for video tape, for there is a long list of ways it can deteriorate:

  • Magnetic particles gradually lose their charge, in a process called remanence decay. The rate depends somewhat on the exact chemistry of the particles used in the tape, but in general if this happens, you can expect some color shift toward weaker hues and loss of detail overall.
  • Magnetic particles may be accidentally demagnetized. This can be from storing too near a magnetic source (like an audio loudspeaker) or even from the playback machine itself, whose heads can be become partically demagnetized if not maintained perfectly. With a poorly maintained VCR, every playback actually erases information from the tape!
  • The lubricant in the binder layer is used up, with each playback. As it erodes, the binder layer itself takes on more wear, which can directly affect the magnetic particles and cause information loss.
  • The binder layer can become a sticky, unplayable mess. The binder's polymers will absorb water (in even a moderately humid environment), in a process known as hydrolysis, and eventually delaminate. Engineers often refer to this as sticky-shed syndrome. Trying to play an affected VHS, VHS-C, or other magnetic tape is an invitation to damage of both the tape and the playback machine.
  • The backing and substrate can become stretched, from multiple rewindings and playback. This causes tracking errors that can dramatically reduce playback quality.
  • Successive recordings can lose information and synch signals. As an analog medium, each generation of recording loses substantial information. If the tape you are trying to preserve was in fact a 2nd or 3rd generation copy, it has already irretrievably lost a great deal of information (see this light-hearted VHS example of what is of course a serious problem).

So how long do video tapes last?

There is no shortage of claims that video tapes "won't last 10 years", almost always from services promoting VHS transfer to DVD! The truth is more subtle, and is suggested by a considerable body of longevity research done specifically on a wide range of video tapes by the National Media Laboratory, Jet Propulsion Labs at Cal Tech, the National Bureau of Standards, The Advanced Development Corporation, and manufacturers Sony and Fuji. First, the risk of hydrolysis, which is potentially catastrophic, is substantially related to how well you store your tapes (see below). Second, the research generally indicates that magnetic tapes (like VHS, VHS-C, etc.) stored well, will experience 10-20% signal loss, purely from magnetic remanence decay, after 10-25 years. While losing 20% is not losing the the entire picture, it may well be the difference between enjoying a memory and simply displaying it. So the sooner your video tapes are digitized, the more signal can be preserved.

What you can  do

In case you can't get your video tapes digitized now, you have some choices about how to store them in the meantime:

  • Keep them cool, but cold.
    The SMPTE standard for preserving video tapes is to keep them at 62 degrees Fahrenheit. This is actually much warmer than is recommended for photos, and that's because at very low temperatures, chemical changes start to happen with the lubricant in a video tape's binder layer.

  • Keep them dry.
    A low relative humidity environment is important to prevent hydrolysis (i.e, to preventing your video tape from becoming a sticky, unplayable mess). As with photos, most experts point to 30% as a good number, which may well be the ambient relative humidity in your home, depending on where you live. Beware, however, of basements and attics.

  • Avoid swings in either temperature or humidity.
    Each change stresses the substrate and backing, and repeatedly doing so will cause tracking problems on playback.
  • Quick Facts

    20%Upper end of video signal loss for a well-stored video tape after 10-25 years.

  • Resources

  • Quick Facts

    5 The number of years ago that a major Hollywood movie was released on VHS. This last release on the format was the 2006 release of "A History of Violence."

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