MagneticMedia AV Workshop Dec 10

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)













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



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



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 #"<)





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



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



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



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





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)



"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)



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)



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



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



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

http://preserve.harvard.edu/

mailto:[email protected]






http://preserve.harvard.edu/

MagneticMedia AV Workshop Dec 10

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