magneticmedia av workshop dec 10
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7/24/2019 MagneticMedia AV Workshop Dec 10
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Magnetic Media
Signal is recorded by moving some magnetic substance (steelwire, disc, or flexible tape coated with ferric oxide) over anelectromagnet that captures the electrical output from amicrophone; playback reverses the process
188 ! "aldemar #oulsonbuilds the first workingmagnetic recorder (wire)
1$ ! Steel tape magneticrecorder developed
1%& ! 'S * + unveil firstcoated magnetic tape recorderat 'erlin -adio Show
1./ ! mpex demos first 0Smade magnetic tape recorder
12% ! Sony markets firsthome "3-
12& ! #hilips introducescompact (audio)cassette
1/1 ! 0S launch of first homevideocassette (04atic)
181 ! Sony unveils 5alkmanportable cassette player
18/ ! Sony introduces 6igitaludio 3ape (63)
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Magnetic Media
7undreds of analog and digital formats include a wide variety ofwire recordings, dictation belts and discs, openreel audiotape andvideotape, audio and video cassettes and cartridges, recordable4ini6iscs, and magnetic soundtracks for motionpicture film
ormats most often found in special collections include openreelaudiotape and videotape, 04atic 9 videotape, "7S, compactcassettes, 63, 4ini6", and 'etacam S#
:early all of these formats may be considered obsolete andtherefore atrisk, even if the carrier itself is healthy
0nderstanding a few basic facts about the nature of theconstituent elements will go a long way toward helping youidentify preservation issues affecting magnetic media
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Magnetic Tape — Composition
ll magnetic tape has
'ase layer (support for magnetic layer) #aper, #"<, cetate, #olyester
4agnetic layer (takes and holds the data)
4aterial may be magnetic particles or magnetic film amma ferric oxide, <hromium dioxide, 4etal evaporate, 4etal
particulate, etc=
Some tape has
'inder layer (holds magnetic particles in place and adds lubricant toreduce playback friction) 0sually some form of polyurethane; sometimes #"<
5eak link in polyester tape (very susceptible to hydrolysis)
'ackcoat layer (reduces static and tape slippage) 4any tapes since the early 18>s have some type of backcoating
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Magnetic Tape — Base Layer #aper
"ery rare; produced 1.>s1&>s
6istinctive blotchy brown paper backing
#olyvinyl <hloride (#"<) -are; produced 1.% to early 1/>s, mainly in ermany
-easonably stable mechanically, but has plastici?er issues Stretches instead of breaking under stress; resulting deformation
is irreversible
<ellulose cetate #roduced late 1.>s to mid 1/>s
6imensionally unstable; prone to shrinkage and breakage
Suffers from @"inegar Syndrome9 (acid hydrolysis), plastici?er issues 'reaks easily under stress
#olyester #roduced from mid 1&>s onward; most common base since 12>s
4echanically robust, chemically stable
:o plastici?er issues, but binder is problematic
Stretches instead of breaking cleanly (like #"<)
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Acetate or Polyester?
3wo easy ways to tell the difference
Dight 3est cetate tape appears translucent when held upto the light; polyester (and #"<) tapes appear opaEue
Snap 3est cetate tape will break without stretching;polyester tape will stretch and curl, but will not break
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Deterioration (1)
Binder degradation <auses #oor storage conditions (high -7), natural aging
Cndicators @Sticky Shed Syndrome9 (powder or gummy residue ontape surface, tape layers adhere, oxide flaking or shedding); strongsmell of @dirty socks9
ffects polyester base tapes, especially 1F$9 openreel videotape
Acetate base deterioration <auses @"inegar Syndrome9 (acid hydrolysis)
Cndicators Strong vinegar smell (acetic acid), tape shrinkage orbreakage, flaking binder layer
4ost likely to occur in openreel G9 audiotapes <an measure severity with 6 Strips
<ontagious Segregate affected tapes, store in cool, dry environment
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Deterioration (2)
Tape Deformation <auses #oor handling and storage conditions, poor tape
wind, misaligned playback eEuipment
Cndicators <inching, stretching, edge damage
Degradation of magnetic particles <auses #oor storage conditions (moisture and pollution),
corrosion
#articularly affects early versions of 4# and 4+ tapes(cracking or delamination of thin magnetic layer)
Mold
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Deterioration (3)
Tape pack problems (loose or uneven wind) <auses misaligned playback eEuipment, poor storage
conditions, exposure to excessive heat or cold
+xacerbated by temperature fluctuations that produceuneven tension across tape pack
Cndicators 3ape pack slippage (popped strands), flange pack,spoking, windowing
Deads to tape deformation, base stretching, edge damage
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Care ! andling (2)
Cassettes and Cartridges 6o not attempt to open tape cartridges
+ngage writeprotect mechanism (prevents accidental rerecording)
Open-eel Tape 7andle only by hub; never touch tape surface
:ever pull the loose end of an openreel tape to tighten thewind
6onJt sEuee?e reel flanges (could damage tape edges)
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"n#ironment and $torage
Store in a clean, cool, dry environment where temperature and -7are constant
void rapid or dramatic temperature or humidity changes (cyclingstresses the layered structure of magnetic tape)
4inimi?e exposure to extreme heat (polyester melts and deforms at
higher temperatures) or high humidity (high temperatures and -7accelerate binder hydrolysis)
Store all magnetic media vertically; do not stack hori?ontally orallow to lean (upright storage helps maintain good tape pack;
stacking can warp cassette shells or tape reels)
Cf possible, segregate acetate materials to prevent contamination of
other materials by acetic acid 6o not interfile recordings of difference si?es (small items get lost,
larger items are exposed to uneven pressure)
-eturn media to storage containers when not in use (to avoid
surface damage and exposure to light)
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Pre%erred Containers — &eneral
-igid, vented, impactresistant containers made ofinert materials
Should protect contents from dust, dirt, and moisture
Should close and latch securely
void paper or plastic sleeves, slipcases, and other
flexible containers (which provide little physicalprotection and may interact chemically with the media)
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Pre%erred Containers — By 'ormat
Apen-eel 3ape -eplace original paper boxes (generally too acidic and do not provide
adeEuate support and protection for the carrier
<ontainer should support reel by the hub
0se unslotted reels if possible
"ideocassettes Ariginal containers generally acceptable if they are rigid, lock securely,
and stabili?e the carrier; do not use original paper or plastic slipcases
<ompact <assettes Store in original :orelco boxes or hinged polyboxes
Small <assette ormats (e=g=, 4inicassette, 63, 4ini6") Ariginal @:orelco9 type containers are acceptable (no good substitute)
Should be grouped in larger boxes to prevent loss and damage
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e*ires +mmediate Attention
"inegar smell (or any strong smell) Dikely indication of advanced deterioration
Ather obvious signs of media deterioration (oxide
shedding, mold)
"isible tape pack issues (loose wind, windowing, spoking,curling)
<racked or broken shells or reels -enders carrier unplayable, could damage tape
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Please Contact ,s
5eissman #reservation <enter
21/.&8&2
httpFFpreserve=harvard=edu
Kane 7edberg HaneLhedbergMharvard=edu
+li?abeth 5alters eli?abethLwaltersMharvard=edu
Di? <offey coffeyMfas=harvard=edu
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