[ARC5] film

[Richard Knoppow]

----- Original Message ----- 
From: "Todd, KA1KAQ" <ka1kaq at gmail.com>
To: <jfor at quikus.com>
Cc: "Roy Morgan" <k1lky at earthlink.net>; "ARC-5 List" 
<arc5 at mailman.qth.net>; <armyradios at yahoogroups.com>; 
<gewhite at crosslink.net>; <milsurplus at mailman.qth.net>
Sent: Sunday, December 02, 2012 8:41 PM
Subject: Re: [ARC5] film


> On Sun, Dec 2, 2012 at 9:07 PM, J. Forster 
> <jfor at quikus.com> wrote:
>
>> Well, it might be available at the Boston Public Library, 
>> but it is just
>> not a useful format to me. I've got 5x7 card file drawers 
>> full of fiches
>> and a couple of readers, but never use them. It's just 
>> too awkward to use
>> a fiche while working on something.
>>
>> I don't even much like a laptop with a .pdf manual, to be 
>> honest. I really
>> don't like to pan and scroll and zoom in and out. I'd 
>> much rather have a
>> HC print.
>>
>
> Convenience and availability/survivability are completely 
> different issues.
> I have a lot of stuff stored on small floppies from 10 
> years ago that my
> current computer won't read (no disk drive). My wife has 
> an Olympus digital
> camera from the 2003-2004 era that the newer (beyond XP) 
> Windoze operating
> systems won't load the software for.
>
> I wonder what the long-term survivability of new CD/DVD 
> disk is? At my
> previous gov't job we had most everything stored on IBM 
> 3590 tape
> cartridges in silos and a lot of round tape. Eventually 
> the round tapes
> went away. IIRC, they figured 99 yrs more or less for 
> viability. I think
> CDs have a potential issue with laser burn, but if the 
> goal is archival
> that wouldn't be an issue.
>
> ~ Todd,  KA1KAQ/4

     Photographic film is relatively stable but the 
stability and life depend on many factors some of which are 
difficult to predict. In black-and-white film the image 
consists of metallic silver suspended in gelatin. Silver is 
vulnerable to oxidation and sulfiding from pollutants in the 
air.  The common method of protecting microfilm images is to 
either convert the silver to silver sulfide, which is very 
stable, or to "tone" it with gold. Gold toning essentially 
plates the silver particles with gold.  A gold toned image 
is very long lived. Sulfide toners treatment has become more 
common because it is much less expensive.  A polysulfide 
toner can be used to partially tone the image with a very 
great improvement in permanence without changing the image 
structure enough to interfere with the very fine detail that 
must be preserved for microfilm. Toned images when properly 
stored have a predicted life of perhaps two centuries.
     The support is a separate problem.  In the distant past 
negatives were coated on glass. Glass is chemically inert 
and does not degrade with age but is obviously mechanically 
vulnerable.  Many glass negatives of historical importance 
have been lose because they were smashed.
     The flexible supports commonly used have in the past 
been of two types, cellulose nitrate and cellulose acetate 
(safety film).  Several variations of the latter have been 
used. Both are unstable. Cellulose nitrate is notorious for 
its fire and explosion hazards.  Safety film, which was 
presumed to be far more stable has turned out not to be. 
Some forms of acetate are less stable than others but none 
are completely stable.  See "vinegar Syndrome" for 
discussions of the problem especially in relation to motion 
picture film but also for still films.
     Polyester base film, such as Kodak Estar, is far more 
stable than any of the older supports and is also more 
dimensionally stable but Kodak no longer supplies film on 
this support.
     At present, photographic film still seems to be the 
best way of preserving images and documents for long periods 
but, like electronic storage methods, it must also be 
renewed occasionally.  The advantage of digital storage, 
assuming a lossless format,  is that the original can be 
regenerated exactly and new generations are exactly like the 
previous ones.  The problem becomes a social one:  one must 
have some organized system of renewing archived material 
often enough to prevent its evanescence. That means 
transferring the entire archive to new formats when required 
to prevent the loss of means of decoding it. The expected 
life of an archive becomes of paramount importance: if one 
expects to preserve material for a century its probable that 
it can be. If one expects to preserve it for a millennium 
its much less likely and longer periods become even less so. 
The entire time of human civilization is probably no more 
than ten or twenty millennia but, of course, we may not wise 
up enough to survive a fraction of that anyway.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com