[pure-silver] Re: Pre-soaking film
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 30 Apr 2010 01:57:15 -0700
----- Original Message -----
From: "Snoopy" <snoopy@xxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, April 30, 2010 1:28 AM
Subject: [pure-silver] Re: Pre-soaking film
Dear Harry et. al.,
harry kalish wrote:
I think their rep at a trade show mentioned that they
had started to
incorporate a wetting agent in their film---roll film
only?, I'm not sure.
it almost certainly is not "roll film only". Roll film and
35mm come
from the same rolls of very wide (several meters wide)
coated emulsion.
Roll films are then cut out of the center strip because
the emulsion
there is more "evenly coated" over a larger area.
35mm are cut from the remaining "edges" of the rolls: as
they are
narrower again the emulsion thickness (i.e. the gelatin
layer) is fairly
even over the area of the film, but there is more
variation between the
rolls, as the big rolls gelatin gets thicker towards the
outside.
This added to the "story" that roll films are
"professional" films, with
a higher consistency. Hence I would bet, that also the
35mm films had
the wetting agent: they come off the same roll.
When I was a student in England our PhotoSoc once visited
Ilfords plant.
The scale of things was awesome. They made millions of
films every MONTH
and used massive saws (all in the dark) to cut up these
huge rolls. Hell
of a noise too.
Love,
Snoopy
Roll film and 35mm film do NOT come from the same master
rolls, for one thing the support is different. 35mm film is
coated on a support which is much thicker than roll film and
sheet film on support which is thicker yet.
I don't know where you got the idea that the emulsion
thicknes varies across the roll. In fact, emulsion thickness
is very well regulated throughout. Most films do not have a
single coating anyway. There is always a substrate to get
the emulsion to stick to the support and usually more than
one emulsion coating. Most films have an anti-abrasion
coating on top of the emulsion. Some color films have twelve
or more emulsion coatings. These must all be coated with
extreme uniformity.
I don't know what Ilford consideres "professional" vs:
something else. Kodak makes all films to a single standard.
Since one of Kodak's largest customers is the motion picture
industry, which requires an extreme standard of uniformity,
it has learned to meet that standard and applies the same
technology to other kinds of films.
All films have various sorts of additives in them some
of which are proprietary. These probably include wetting
agents. Most motion picture stocks are intended for machine
processing and I am not certain if a wetting agent is
desireable in them.
Some wetting agents, notably the ones used in Photo Flo
are not suitable for direct use in developers but there are
others that are.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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