Magnetic Media
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Signal is recorded by moving some magnetic substance
(steel wire, disc, or flexible tape coated with ferric oxide)
over an electromagnet that captures the electrical output
from a microphone; playback reverses the process
1898 – Valdemar Poulson
builds the first working
magnetic recorder (wire)
1929 – Steel tape magnetic
recorder developed
1935 – BASF & AEG unveil
first coated magnetic tape
recorder at Berlin Radio Show
1947 – Ampex demos first
US-made magnetic tape
recorder
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1963 – Sony markets first
home VTR
1965 – Philips introduces
compact (audio)cassette
1971 – US launch of first
home videocassette (U-Matic)
1981 – Sony unveils Walkman
portable cassette player
1987 – Sony introduces Digital
Audio Tape (DAT)
Magnetic Media
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Hundreds of analog and digital formats include a wide variety
of wire recordings, dictation belts and discs, open-reel
audiotape and videotape, audio and video cassettes and
cartridges, recordable MiniDiscs, and magnetic soundtracks
for motion-picture film
Formats most often found in special collections include openreel audiotape and videotape, U-Matic ¾” videotape, VHS,
compact cassettes, DAT, MiniDV, and Betacam SP
Nearly all of these formats may be considered obsolete and
therefore at-risk, even if the carrier itself is healthy
Understanding a few basic facts about the nature of the
constituent elements will go a long way toward helping you
identify preservation issues affecting magnetic media
Magnetic Tape — Composition
All magnetic tape has:
 Base layer (support for magnetic layer)
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Paper, PVC, Acetate, Polyester
Magnetic layer (takes and holds the data)
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Material may be magnetic particles or magnetic film
Gamma ferric oxide, Chromium dioxide, Metal evaporate,
Metal particulate, etc.
Some tape has:
 Binder layer (holds magnetic particles in place and adds
lubricant to reduce playback friction)
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Usually some form of polyurethane; sometimes PVC
Weak link in polyester tape (very susceptible to hydrolysis)
Backcoat layer (reduces static and tape slippage)
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Many tapes since the early 1980s have some type of backcoating
Magnetic Tape — Base Layer
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Paper
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Polyvinyl Chloride (PVC)
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Rare; produced 1943 to early 1970s, mainly in Germany
Reasonably stable mechanically, but has plasticizer issues
Stretches instead of breaking under stress; resulting deformation
is irreversible
Cellulose Acetate
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Very rare; produced 1940s-1950s
Distinctive blotchy brown paper backing
Produced late 1940s to mid 1970s
Dimensionally unstable; prone to shrinkage and breakage
Suffers from “Vinegar Syndrome” (acid hydrolysis), plasticizer issues
Breaks easily under stress
Polyester
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Produced from mid 1950s onward; most common base since 1960s
Mechanically robust, chemically stable
No plasticizer issues, but binder is problematic
Stretches instead of breaking cleanly (like PVC)
Magnetic Tape — Magnetic Layer
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Gamma Ferric Oxide
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Chromium Dioxide
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Found to interact with polyester urethane to accelerate acid hydrolysis
Type II Compact Cassettes, analog video formats
Metal Evaporate
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Stable
2” Quad videotape, Type I Compact Cassette
Has no binder, but does have lubricant to reduce friction
Type IV Compact Cassettes, DAT
Metal Particulate
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Prone to oxidation
Type IV Compact Cassettes, digital video formats, DAT, Hi-8
Acetate or Polyester?
Two easy ways to tell the difference:
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Light Test: Acetate tape appears translucent when held up
to the light; polyester (and PVC) tapes appear opaque
Snap Test: Acetate tape will break without stretching;
polyester tape will stretch and curl, but will not break
Deterioration (1)
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Binder degradation
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Causes: Poor storage conditions (high RH), natural aging
Indicators: “Sticky Shed Syndrome” (powder or gummy residue on
tape surface, tape layers adhere, oxide flaking or shedding); strong
smell of “dirty socks”
Affects polyester base tapes, especially 1/2” open-reel videotape
Acetate base deterioration
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Causes: “Vinegar Syndrome” (acid hydrolysis)
Indicators: Strong vinegar smell (acetic acid), tape shrinkage or
breakage, flaking binder layer
Most likely to occur in open-reel ¼” audiotapes
Can measure severity with A-D Strips
Contagious: Segregate affected tapes, store in cool, dry environment
Deterioration (2)
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Tape Deformation
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Degradation of magnetic particles
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Causes: Poor handling and storage conditions, poor tape
wind, misaligned playback equipment
Indicators: Cinching, stretching, edge damage
Causes: Poor storage conditions (moisture and pollution),
corrosion
Particularly affects early versions of MP and ME tapes
(cracking or delamination of thin magnetic layer)
Mold
Deterioration (3)
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Tape pack problems (loose or uneven wind)
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Causes: misaligned playback equipment, poor storage
conditions, exposure to excessive heat or cold
Exacerbated by temperature fluctuations that produce
uneven tension across tape pack
Indicators: Tape pack slippage (popped strands), flange
pack, spoking, windowing
Leads to tape deformation, base stretching, edge damage
Care and Handling (1)
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Never touch the surface of a magnetic recording
Do not drop or subject to sudden shock (prevents
breakage and other problems with reels and cassette
shells, container breakage, and tape pack distortion)
Never leave media in playback equipment (prevents
excessive heat exposure and mechanical damage)
Keep media away from stray magnetic fields (most
important for wire recordings)
Labelling should not hinder tape transport in any way
Inspect media periodically for signs of deterioration
Care & Handling (2)
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Cassettes and Cartridges
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Do not attempt to open tape cartridges
Engage write-protect mechanism (prevents accidental
re-recording)
Open-Reel Tape
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Handle only by hub; never touch tape surface
Never pull the loose end of an open-reel tape to tighten the
wind
Don’t squeeze reel flanges (could damage tape edges)
Environment and Storage
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Store in a clean, cool, dry environment where temperature
and RH are constant
Avoid rapid or dramatic temperature or humidity changes
(cycling stresses the layered structure of magnetic tape)
Minimize exposure to extreme heat (polyester melts and
deforms at higher temperatures) or high humidity (high
temperatures and RH accelerate binder hydrolysis)
Store all magnetic media vertically; do not stack horizontally
or allow to lean (upright storage helps maintain good tape
pack; stacking can warp cassette shells or tape reels)
If possible, segregate acetate materials to prevent
contamination of other materials by acetic acid
Do not interfile recordings of difference sizes (small items
get lost, larger items are exposed to uneven pressure)
Return media to storage containers when not in use (to avoid
surface damage and exposure to light)
Preferred Containers — General
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Rigid, vented, impact-resistant containers made of
inert materials
Should protect contents from dust, dirt, and moisture
Should close and latch securely
Avoid paper or plastic sleeves, slipcases, and other
flexible containers (which provide little physical
protection and may interact chemically with the media)
Preferred Containers — By Format
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Open-Reel Tape
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Videocassettes
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Original containers generally acceptable if they are rigid, lock securely,
and stabilize the carrier; do not use original paper or plastic slipcases
Compact Cassettes
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Replace original paper boxes (generally too acidic and do not provide
adequate support and protection for the carrier
Container should support reel by the hub
Use unslotted reels if possible
Store in original Norelco boxes or hinged polyboxes
Small Cassette Formats (e.g., Minicassette, DAT, MiniDV)
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Original “Norelco” type containers are acceptable (no good substitute)
Should be grouped in larger boxes to prevent loss and damage
Requires Immediate Attention
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Vinegar smell (or any strong smell)
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Likely indication of advanced deterioration
Other obvious signs of media deterioration (oxide
shedding, mold)
Visible tape pack issues (loose wind, windowing, spoking,
curling)
Cracked or broken shells or reels
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Renders carrier unplayable, could damage tape
Please Contact Us
Weissman Preservation Center
617-495-8596
http://preserve.harvard.edu
Jane Hedberg jane_hedberg@harvard.edu
Elizabeth Walters elizabeth_walters@harvard.edu
Liz Coffey coffey@fas.harvard.edu