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ARSCLIST  July 2003

ARSCLIST July 2003

Subject:

Re: Long-term/preservation audio (delayed)

From:

George Brock-Nannestad <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Tue, 29 Jul 2003 17:20:07 +0200

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (55 lines)

From: Patent Tactics, George Brock-Nannestad

Steven C. Barr wrote:

> However, I have a number of shellac 78's dating back into the 19th century,
> and they show no signs of deterioration. Are there any VERY-long-term issues
> as far as the lifespan of shellac records is concerned, provided they are
> stored under reasonable care (and aren't dropped)?

----- shellac records are ca. 80 % rottenstone, a mineral, and the binding
agent is shellac, a natural polymer that crosslinks (gets stronger) over
time. There is no doubt that ordinary oxidising agents, such as air, ozone,
aided by actinic radiation (sunlight) will break down the shellac to some
extent, however because they did not want the records to look like concrete,
carbon black was added to the mix, and similar to the carbon black in rubber
for tyres, it protects against the light.

So what remains as damaging agents: humidity, humidity, humidity, and
humidity. The first is because of lack of cleanliness, there are fibrous
materials (well, the original Duranoid button material had cotton flock
deliberately added for strength) that swell when they absorb moisture, and so
breaks the surface. The second is that some of the rosin components added for
mold release and - perhaps - lubrication during replay are not totally
impervious to water. The third is that microorganisms need not only their
preferred food, but also a quite specific degree of humidity, individual to
the strain, so they may thrive. The fourth is the label that was printed with
pigments that would tolerate the high temperature, but which are generally
not waterfast.

Temperature is another problem with shellac as a binder: it softens, but less
when the cross-linking has progressed. So it is easier to straighten dish-
shaped records in an early century of its life. However, bear in mind that in
later years of the shellac era, a lot of subsitute polymers were used,
acetate types being mixed in, partly because of wars.

Solvents is a third problem.

In conclusion: if you keep your shellac records dry and cool (or at least
flat when hot) and remote from solvents, you may regard your records as being
of archival quality.

Wouldn't metal also be
> likely to corrode or be otherwise damaged?

----- nickel (at least solid) and silver have a propensity to grow whiskers:
material redistributes itself under certain conditions of humidity to form
very long and narrow single crystals.

But cool and dry, and you are all right.

Kind regards,


George

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