On Thu, Mar 29, 2018 at 11:29 AM, Jon Elson via cctalk < cctalk@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
