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Re: "WHITE POWDER"



Dear Dave,

The first thing you have to determine is the source of the powder, which can
be done with a powerful magnifying glass.  PTR roller dust from defective,
worn out, or misaligned rollers look just like tiny eraser crumbs.  We've
encountered dust from all three of the above causes with a couple of brands
of rollers.   We have also seen problems caused by plastic PTR roller
bearings falling apart, and from the backsides of the rollers rubbing on the
arms.

Excessive moisture in the film cleaning solution can cause a situation where
the film will shed tiny white "flakes" all over everything, as can
indiscriminate cleaning of negative and print in the same machine (prints are
often waxed so they'll go through projectors easily; this wax can mix with
the film cleaning fluid and get onto whatever is cleaned subsequently).
 While on the topic, it turns out that now that new trichlor is no longer
readily available, a lot of suppliers are selling recycled material or
trichlor mixed with other stuff as a substitute.  These "substitutes" will
work for cleaning film, but you really have to pay attention to the chemical
analysis and to the moisture content of what you're getting; it sure ain't
like the "good ole days" when you could pop the cork on a barrel of trichlor,
dump it into the Lipsner, and go.

Mechanical problems such as binding or misaligned rollers and skid plates
will abrade the edges of film, leaving a white powder that looks like fine
plastic filings or sawdust.  But usually this will only be apparent at the
point where it is being created; it doesn't tend to get all over everything
unless it really gets a chance to build up.  Your message indicates that the
problem is happening on more than one machine, so I would not immediately
think it was a mechanical problem.

Finally, I'd like to point out that this lab has been in the process of
changing from trichlor to perc film cleaning machines for more than a year
now.  So in that time, we've actually had both types going side-by-side, and
this has not resulted in any problems with white powder, or with unusual wear
of capstans or PTR rollers on our Ranks.  Perc makes an excellent film
cleaner so long as it is bought from a reputable supplier (and not the corner
dry cleaners'), and is handled properly.

Christopher Bacon
DuArt Film & Video