Re: could it be bubbles?

[boblong@xxxxxxxxxxx (Robert Long)]

On Tue, 03 Dec 1996 09:19:24 +0000 (GMT), [oops, I lost the original,
so I don't know who] wrote:

|I just got a film back from the lab and there are lots of undeveloped =
spots
|on the film, about 1mm in diameter.  These are clear on the negative, =
and
|some have a tiny developed spot in the centre.
|
|They are randomly distributed on the surface ofthe film, with some
|clustering and some frames nearly free of em.

My guess:  Yes, it's bubbles.  Bubbles can form both on the film
surface and within the emulsion.  The standard recommendation that you
rap the film tank sharply after adding the developer is intended to
get rid of adhering bubbles.  The bubbles in the emulsion (which
usually cause just clear pinholes) are theoretically caused, or at
least exacerbated, by the use of an acid stop bath.

I suspect that if your have clear circles with dense spots at their
centers it is not becuase the centers were developed, but because they
*weren't* developed--or fixed.  The clear ring could be caused by lack
of development followed by removal of the undeveloped halide by fixer
that penetrated farther beneath the bubble than the developer had
done, but not all the way to the center.  But it astonishes me that
bubbles would have remained in place throughout the
developer/agitation/rinse/fix process.

=46or some reason, IR films seem to be more prone to bubble problems
than other films.  The recommendation that the tank be rapped sharply
and that a plain water rinse be used in place of an acid stop bath
have both appeared here, and elsewhere, to help solve the problem.  In
addition, some recommendations include the use of distilled water
only--never tap water--in all solutions used to process IR films.
I've used filtered water for years with no problems, but some color IR
films I sent to a commercial lab years ago came back full of pinholes.

Bob Long
(boblong@xxxxxxxxxxx)

------------------------------

Topic No. 13