August 29, 2006, from Lloyd Erlick,

Richard's post jogged the memory of the
following post from Douglas Nishimura a few
years ago:

_______________________________________________
From dwnpph@rit.edu Mon Sep 04 01:57:38 2000
Newsgroups: rec.photo.darkroom
Subject: Warning: Negative base deterioration
From: Douglas Nishimura <dwnpph@rit.edu>
Date: Mon, 04 Sep 2000 01:57:38 -0400

I was trying to think of a subject line that
would catch peoples'
attention. I hope it worked.

If you haven't been using polyester based
film (such as Kodak Estar base
films), then I expect that most of you won't
have any negatives left
within a few decades. Let me give you the sad
story first before I talk
about the whys and hows.

I got a call around 1992 or so from Evelyn
Hoffer (I hope that I spelled
that right) a photographer in New York who
was known for her coffee
table books in the 1950s and 60s of European
cities. She called because
she went into her negative collection and
found that they were all badly
distorted and the emulsions were lifting off.
We had been researching
this problem since 1988 and were very aware
of what the problem was. It
was probably one of most difficult things
that I've done -- to tell her
that her life's work (other than what books
and prints were already out
in the world) was gone and there was nothing
that could be done. A few
could be saved by special methods, but it's
so labor intensive that of
her thousands of negatives, it would only be
worth treating a couple.

Think about it.....this was only 30 years or
so.........

Any film that you're shooting that isn't
polyester (also called
poly(ethylene terephthalate), trade names
include Estar and Mylar) then
you're on cellulose triacetate. All of the
cellulose acetate film bases
are made by taking cellulose (the main
constituent of paper and trees)
and modifying with acetic acid. (I'm
oversimplifying here, but this is
the general idea.) This is why it's cellulose
acetate. Kodachrome film
was on a variation of this base until about
1976 and then it switched to
triacetate. Ektachrome sheet film was also on
another variation, but all
of these bases behave in the same way. The
plastic base reacts with
water and the humidity in the air is
sufficient. The water in the
presence of acids (and alkalines) pulls off
the acetates as acetic acid
(or vinegar) and you can smell it. Water
alone can also do this, but the
acid or alkaline acts as a special kind of
accelerator called a
catalyst. A catalyst makes reactions much
faster without being consumed.
(This is why the catalytic converter on your
car only needs a tiny bit
of platinum.) Consider then that one acid and
water goes in and two
acids (the original plus a vinegar) comes
out. Those two can go into a
reaction to produce four acids and so on and
so on. This is what we call
an autocatalytic reaction...The stuff is
generating it's own accelerator
to destruction. If we measure the
deterioration over time, it starts out
very slowly and slowly gets faster.
Eventually it generates enough acids
that it reaches what we call the
"autocatalytic point" and the reaction
really accelerates and gets faster and
faster. To visualize what I see
when we measure acidity over time, take a
piece of paper and draw an x
and y axis. Now draw a line that starts just
above the x axis and rises
at maybe a 10 degree angle. At the end of
this line draw a line that is
almost at 90 degrees. Round the sharp angle
where the two lines meet.
This is more or less how the reaction goes.
Right at the elbow is what
we call the auto-catalytic point.

Now...at the same time, acids and water can
also react along the length
of the long plastic molecules causing them to
break into shorter pieces.
This reaction is acid (or alkaline)
catalysed, but is not autocatalytic.

Removal of the large acetate groups as acetic
acid vapors causes the
film base to shrink. It will ultimately
shrink about 10% to 15%. At the
same time, the gelatin emulsion is trying to
stay attached, but it's not
shrinking so eventually the adhesion between
the base and the emulsion
gives out and we see this as "channelling."
You literally find tunnels
formed by the emulsion (on top) and the
separated base on the bottom
often about 1/8 inch in diameter. Sheet films
with an anti-curl layer
will also do that on the anti-curl layer side
as well. Breaking of the
plastic molecules into short pieces meanwhile
causes the base to get
brittle. I've shocked my students by giving
them a sheet of deteriorated
film and letting them flex it. It eventually
has the flexibility of
fresh potato chip. I've crumbled a negative
between my fingers like
crisp bacon. Meanwhile plasticizers in the
base become incompatible and
they start coming out as perhaps feathery
crystals or as oily liquid
filled blisters, or as solid plugs. The
feathery crystals are about the
most common plasticizer, tri-phenyl
phosphate. The oily liquid
plasticizer is a phthalate, often
dimethoxyethylphthalate.

How fast can this happen? If you stored your
negatives constantly at a
comfortable 70F (21C)/50% relative humidity,
we would expect to see
fresh acetate film hit the autocatalytic
point in about 40 years. In the
case that I mentioned above, every summer she
would close-up her
Manhattan apartment and head to Europe so the
negatives literally baked
in the humid New York City heat which greatly
reduced the life of her
negatives. To give you an idea about how fast
this thing can go, let me
give you an example. Suppose that we track
the acidity in the base over
time. It starts out very very close to zero
and at the auto-catalytic
point has x amount of acid. Now I mentioned
that at 70F (21C)/50% RH it
will take about 40 years to create x amount
of acid. How long do you
think it would take, if we left it stored
under the same conditions, to
double in acidity or to reach 2x acidity? Let
me tell you that it will
be about another 5 years....and to increase
to 3x acidity would take
around another 2 years. Most of you don't
have 70F/50% RH storage.
Temperature and humidity play a big role. If
you were at 75F (24C)/50%
RH rather than 40 years, it would take
roughly 25 years to reach the
autocatalytic point and another 4 years or so
to double. Humidity also
plays a big role (since the reactions need
water.) If you were at
70F/80% RH not only would I worry about mold,
but you'll reach the
autocatalytic point in about 17 years.
However, if you were in a very
dry place at say 20% RH, it could take about
90 years to reach the
autocatalytic point. I should add that the
autocatalytic point isn't the
end of life for your negative. It'll stink,
but will still be printable.
Even at double the acidity, you should still
be able to use the film,
but time left is very short.

Now before people start calling the
manufacturers to complain, it isn't
their fault. In the early 20 th century when
acetate bases came out to
replace nitrate, they ran accelerated studies
and found that the acetate
hardly deteriorated at all while the nitrate
was falling apart like
crazy so they thought that it was pretty darn
stable. Unfortunately they
didn't realize that the reaction needed
moisture and they were running
dry oven tests. (The RH was probably only
around 5% to 8%.) They started
getting complaints in the 1950s or 60s, but
they were all from tropical
countries (parts of India, south-east Asia,
South America,....) and they
thought that it would only happen in tropical
countries. Much to their
surprise it started showing-up in north
america starting in the early
1980s. People said that the triphenyl
phosphate also reacts with
humidity to form phenol (aka "carbolic acid")
and phosphoric acid. This
was true, but even film that contained
different plasticizers also
deteriorated. Some people said that it was
the nitrate subbing layer.
[Gelatin didn't stick very well to cellulose
acetate, but it did to
cellulose nitrate and cellulose nitrate also
stuck very well to
cellulose acetate so they used a very thin
layer of cellulose nitrate as
a glue to stick the emulsion to acetate bases
up until at least the
early 90s or so.) Well, research showed that
it wasn't the nitrate
subbing either because film with and without
the subbing layer
deteriorated at about the same rate. (More
recently companies have found
how to make gelatin stick and the nitrate
subbing layer isn't used
anymore.) Some people worried that it was
processing since people were
using acid fixing baths and acid stop baths.
Well, it's not the
processing either. I have a large box of
unprocessed sheet film that
just stinks.

About the only thing that you can do is to
store your negative at a
reasonably cool temperature. In fact the ISO
and ANSI standards
recommend that collections store their
acetate negatives below 45F (and
only then if they can be stored between 20%
and 30% RH otherwise they
have to be even colder.)

One of the lessons that we've learned about
this is that bad conditions
count for more than good conditions so even
if your place is pretty good
most of the year, but bad during the summer,
the summer will kill you.
Consider my apartment. I keep it pretty cool
during the winter (I like
the cold) and it sits at 55F and a humidifier
keeps it around 50% RH. If
my apartment was like that all the time, my
negatives wouldn't reach the
ACP for about 100 years. During the summer
though its often 85 or worse
since I don't have a good flow of air through
the place (due to window
locations.) The humidity also gets pretty
high (although my bedroom is
air conditioned.) At 85F/70% RH I should
reach the ACP in about 9 years.
What are the comparable effects of these two
extremes? We'll ignore the
spring and fall and for simplicity say that
my apartment is at each
condition roughly half the time (all other
times are somewhere in
between.) The overall effect is that my
negatives (if I stored them
there) would reach the ACP in 16 or 17 years.
They would be toast in
less than 25 years. Now most people don't
keep their places as cold as I
do in the winter and most people in Rochester
would find even less time
before they were in trouble.

This is not to say that every negative stored
under these conditions
will suffer this fate. We find it to be like
people. You find the odd
90-year old who still smokes a pack a day.
Who knows why they're still
around? We also find the odd negative that
does better or worse that we
would expect. However, anecdotal evidence
from collections suggest that
on average, our estimates are pretty good. We
run a seminar every August
and back in the early 1990s I asked how many
people (there were usually
around 50 participants) had acetate
deterioration in their collections
and a few people put up their hands. Each
year the number of hands
increased and now there's virtually no one
who says no (unless they
don't have any acetate negatives.)

The motion picture industry spent millions on
cold storage in the past
10 years just because of this problem. They
call it "vinegar syndrome"
for good reasons. People there ask how much
vinegar can come out of film
so I ran a calculation based on typical
triacetate film -- 1000 ft of 35
mm. This is roughly equivalent to 200 rolls
of 36-exposure 35 mm film or
roughly 200 8 X 10 sheets. Ask yourself how
much vinegar you might
expect if we took all of the acetate off of
the film and turned it into
aqueous vinegar (as you buy it in the store.)
The amount is just a tiny
bit less than one US gallon. You can smell
acetic acid at very low
levels by the way-- roughly 1 ppm in the air.

Polyester will more or less do the same thing
(producing ethylene glycol
(anti-freeze) and terephthalic acid.) However
if it takes say 100 years
for acetate to reach some point of
deterioration at 70F/50% RH, under
the same conditions, it would take polyester
somewhere between 500 and
10,000 years to reach the same state. This is
why we don't tend to worry
about it with polyester.

You may ask why the companies don't switch
totally to polyester. They're
certainly trying to, but it's not necessarily
all that easy. One problem
that needs to be dealt with is know as
core-set. (This is different from
a corset. :^)) If you roll plastic film
tightly onto a small
reel....like a 35 mm spool...you cause
stress. The outside of each lap
of film is larger than the inside of the lap.
(We see this at the
Olympic field events. The runner in the
inside lane has a shorter
distance to run so must start further back to
compensate.) Inside the
plastic these stresses cause the polymer
(plastic) molecules to slide
against each other to relieve the stress.
This is known as "cold flow."
The plastic is literally changing shape at
room temperature. The result
is curly film. I remember when I was in high
school standing in the dark
with this roll of incredibly curly film
trying to get it onto a film
real. Ack. Cellulose acetate takes on
core-set faster than polyester.
However, what happens to the curly roll after
processing? It hangs nice
and flat (pretty much) certainly nothing like
the horrible mess you were
trying to get onto the reel. This is because
acetate film absorbs a fair
amount of water during processing (a few
percent by weight) and this
causes the core-set to be released.
Polyester, on the other hand, only
absorbs a fraction of a percent water by
weight during processing so 35
mm polyester film would come out of
processing about a curly as it went
in. Imagine how hard it would be to print
curly negatives. As far as I
know, the only 35 mm polyester film on the
market right now is Techical
Pan. The industry is working on the problem
though and may even now have
a solution. (And they may be producing much
more 35 mm polyester film.)
Polyester, as I've mentioned in regard to
photo enclosures, is also
fairly expensive and tends to dull cutting
blades pretty easily.

By the way, you may hear of people saying
that this base deterioration
is just a "diacetate problem." It's not true.
When diacetate film was
made starting in the late teens they didn't
add as much plasticizer and
one of the consequences was a larger degree
of solvent pooling. Have any
of you ever tried to dry tomatoes? If you
don't cut them up, the outside
dries quickly forming a hard shell outside.
Water from the inside can't
pentrate this hard shell so the tomato stays
wet inside and eventually
rots. Acetate film base has the same problem.
It's cast by mixing the
plastic with methylene chloride (and a few
other solvents) to form a
viscous syrup called "dope." This is poured
onto a very large,
continuously rotating wheel. As the wheel
turns, heaters and fans
(effectively) evaporate off the solvents so
that by the time the wheel
has made one rotation, the film base can be
peeled off for coating. The
solvents evaporate off the surface very
quickly but this forms a solid
outside while there's still solvents trapped
inside that can't get out.
One of the things that the plasticizer does
is to reduce the amount of
trapped solvent. (It's primarily added as a
fire retardant.) By the time
you get the film, it contains around 2%
solvent by weight and this
slowly evaporates out over time. (Causing the
film to slowly shrink very
slightly.) When they made diacetate, they
didn't include as much
plasticizer so the there was a greater amount
of solvent loss shrinkage
and since acetate deterioration also
manifests itself as a shrinkage,
people assumed that they were the same
problem. (Diacetate will also get
acetate deterioration, but the initial rapid
shrinkage found with
diacetate was solvent loss and not base
deterioration.) On a historical
note, nitrate film was the first cellulose
based film to be case on a
wheel. Prior to that they used a glass table
at Kodak that was made from
a single piece of perfect glass 200 feet long
and 40 inches wide. The
glass had to be absolutely flat with no
scratches. In the afternoon they
poured the nitrate dope onto the table and
then they turned on big fans
and opened all the windows. (Obviously there
was no EPA then.) In the
morning, they closed everything up and poured
on the emulsion (in the
dark.) When the emulsion had set, they peeled
the film and cut it up
then poured the next batch of base. Now as
bad as this sounds, prior to
this, they used to shave sheet film base off
a block of cellulose
nitrate.

One last thing.... polyester doesn't suffer
from solvent loss shrinkage
because it has to be melt cast rather than
solvent cast. The melt is
extruded into a sheet and then undergoes
several physical modifications.
One thing that they do is known as biaxial
orientation. They take the
extruded film and they heat it up and pull it
in the length direction
they repeat the process in the width
direction as well. I never can
remember the order and it may be width first.
What this does is causes
the plastic molecules to line-up in the plane
of the film. (If this was
a bed full of kids, all of them are lying
down in different directions,
but no one is standing up.) The last thing
they do is to add dimensional
stability by partly crystalizing the plastic.
(For the chemists out
there, of course that can't be done, but
parts of the molecule end-up in
a closest packing state.) If this wasn't
done, if the film was heated
(say in a projector), the base would shrink.

Anyway, I'm hoping that if I can spread the
word through the world of
photographers I won't have to tell anyone
else that there's nothing left
of their life's work.

-Doug
Douglas Nishimura
Research Scientist
Image Permanence Institute