Digitising collections of microfiche - Re: Looking for opinions...

[Shaun Halstead]

On Thu, Mar 29, 2018 at 11:29 AM, Jon Elson via cctalk <
cctalk at classiccmp.org> wrote:
>
> Huh?  DEC service and software listings on Diazo?  Hmmm, you are right!  I
> always thought these were silver film, but just took a look and they are
> very dark blue Diazo.  On the other hand, these are VMS 4.2 fiche, so QUITE
> old, and look totally brand-new.  So, we have a few years yet to find a way
> to read them.
>

  Diazo duplicating film comes in a variety of dye colors.  Most of what we
used at my old shop was black, or the typical, recognizable blue.  Silver
duplicating film is far more resistant to fading, but is usually considered
to be too expensive for regular use, though some customers did specify
silver working copies.  Silver duplicating film is a little different from
silver original film, and it isn't always easy to tell whether a piece of
silver film is original or silver duplicate.
  As for diazo fade, there are several variables involved beginning before
the duplicates are ever created.  Age and storage conditions of the raw
film, light contamination (diazo is considered light-safe, but unprocessed
film will fade), heat and ammonia exposure prior to use and during
processing, storage conditions (heat, light, handling, humidity) after
processing.



> I am familiar with that frosty Diazo fiche that are very pale blue color,
> wouldn't be surprised if those faded.  They were never intended for
> archival storage.
>

  This is could be faded film, or it could have been a bad copy to start
with.  Insufficient ammonia during processing will cause a thin or pale
appearance.

  Another duplicate media I've encountered, though never in service
manuals, is vesicular.  It has a very distinctive appearance and texture,
and can be very difficult to scan, due to a low contrast.

--Shaun