Postulate
Don't tell an archivist how to store film. He knows what to do,
and he has many years of experience. If you tell him anything
new and daring, he won't believe you. If you tell him anything
with a scientific basis, he still won't believe you, but he might
start wondering.
If you are too convincing he may conduct his own investigation,
so you don't catch him off base again.
Why bother to carry out research?
Even so, there is reason to research, to objectively study the
way things are done, and to correlate the good and bad - simply
because the film archivist is in the unhappy situation of having
inherited "the way to do things".
It was never intended, a hundred years after the invention of
film, that we should witness its disintegration.
A super-fragile medium
The archivist is fighting the sins of the past. Perhaps he therefore
takes the state of the art of the past for the best solution instead
of looking at new solutions. So he cannot be blamed for having
done anything wrong - or can he? As most archives are members
of one or another association they rely on the recommendations
given by the advisory committees dealing with his particular problems.
Archiving is a world problem and the associations have members
from almost every country in the world. But when it comes down
to even following the recommendations then the situation is somehow
different. Even separating nitro from acetate is in many places
neglected.
Funding is a world problem for archives, and a poor excuse.
On film can state of the art... (1)
Extract from Archivum April 1992. ( Now Archivum Danicum).
The Center for Archival Polymeric Material at Manchester Polytechnic
in England ( now the Manchester Metropolitan University) has been
conducting research into the degradation and stabilization of
film for the past 5 years.
Film cans
The studies have highlighted the importance of the storage enclosure.
Tin coated or polymer coated metal cans are unsuitable. Iron must
not be used under any circumstances because it catalyses the oxidation
processes in the polymer. Aluminum is better, but is also a weak
catalyst. Paper/cardboard containers are unsuitable because they
generate acids during storage which can be damaging in time; they
should not be used.
Apart from glass (basis type) which has obvious practical disadvantages,
plastics- and in particular the polyolefins- are the most suitable
and most economic materials for archive film containers. They
have the advantage of a simple structure with only carbon and
hydrogen atoms in their molecular make up.
High-density polyethylene and polypropylene are the best choices,
since they act as effective barriers to oxygen diffusion.
All this was written in Archivum 2 years ago and at that time
a new project was launched to study a number of film cans and
their behavior with film.
This project from Manchester Metropolitan University is now public
and here is an extract from it.
Chapter Six
Experimental
6.10 Analysis of the "Plastic" Can (2)
The effect of different storage containers on the stability
of cellulose acetate based motion picture film was investigated.
In this investigation, samples of black and white processed 35mm
motion picture film were rolled in reels to simulate archival
storage. They were then placed in appropriate"plastic"
cans and aged in an environment of 50% RH/70°C for 100 days.
Samples of the film were taken for analysis every 5 days. As a
comparison a sample of motion picture film was artificially aged
in a metal container for the same period of time.
A similar study investigated the effect of FICA bags on the stability
of motion picture film enclosed within. As a comparison processed
black and white cellulose acetate based motion picture 35mm films
were aged in tin-plated iron containers under dry conditions at
45% RH at 80°C. These films were then compared with 35mm film
in the FICA bags after a period of 60 days.
Samples of cellulose acetate based motion picture film were also
artificially aged at 90°C/100% RH, for a period of 6 weeks
in contact with pressed sheets of both polypropylene and polyethylene.
These sheets contained no additives after processing. The growth
of peroxide levels of these sheets was then investigated.
Type of Can and Specification
Metal Can
Dancan 1
in High Density Polyethylene (HDPE)
Copper Phthalocyanine Pigment (Blue Green) 2%
Titanium Dioxide-Rutile 0,2%
No Flame Retardant
Trace level of antioxidant <0,05% put in by Manufacturers.
Dancan Stabilized
High Density Polyethylene (HDPE)
Stabilization Formula
Blue Pigment as above
Titanium Dioxide-Rutile 0,2%
No Flame Retardant
Dancan Copolymer
As Dancan 1 except Polypropylene Copolymer (PP)
Library of Congress Can
Polypropylene Copolymer
Carbon Black Coloring Agent
Titanium Dioxide
Flame Retardant Ethylene bus (disbromoboranne)
Dicarboxmide 3-4%
Antioxidant Distearyl Thiopropionate (DSTDP) 1%
Paper Carton
Cardboard Carton obtained from Denmark
FICA Bags
Polyethylene Coated Bag/Vacuum Sealed
7.4 The Effect of Storage Containers on Cellulose Acetate
Based Motion Picture Film
The effect of the different storage containers on % viscosity
retention are illustrated in figures 7.32-7.36. It can be seen
that with all the containers investigated there is a loss in the
viscosity of the motion picture film in each case over the time
period studied. Although aging was undertaken at an elevated temperature,
this was well below the glass transition of the cellulose acetate
polymer and so the same relationship between the films at ambient
conditions would be expected. As mentioned in section 7.1.1. viscometric
data may be considered to be an indicator of both chain scission
and deacetylation thus indicating degradation of the motion picture
film.
The first interesting point to note is that the viscosity retention
of the motion picture film aged in the metal can has been maintained,
relative to each of the alternative "plastic" cans.
In the case of cellulose acetate based motion picture film a 10%
loss in viscosity is considered to indicate that the film has
suffered an irrevocable loss in its physical properties. From
7.32 it can be seen that both the metal can and the Dancan 1 (HDPE)
can have not suffered to this extent. This is also true for the
other cans investigated, the only exception being the Library
of Congress can.
The first difference between the Library of Congress (PLIO) can compared with the other Dancan cans is that this particular can is manufactured using polypropylene. One possible speculative mechanism for what appears to be a detrimental influence of the polypropylene compared with that of polyethylene is associated with its auto catalytic mechanism on oxidation.
A typical mechanistic scheme for the oxidation of for the combustion of liquid hydrocarbons is illustrated by the Bolland-Gee auto oxidation process.
| Sample | Appearance | % Moisture Regain | pH |
| 45% RH/Metal Can | Good Condition | 4,33 | 5,44 |
| Dry Cond/Metal Can | Brittle, Acetic Odor | 4,92 | 4,07 |
| FICA (1) | Very Brittle, Strongly Acetic | 6,32 | 3,36 |
Finally, one possible explanation for the different effect of the polypropylene can compared to the other cans investigated involves looking at the effect of the other components of the can itself. The Library of Congress can contains the flame retardant ethylene bis (dibromoborane) dicarboximide (3-4%). It is possible that this component has had a detrimental effect on the % viscocity retention of the cellulose acetate based motion picture film.
Any changes in the acidity of the cellulose acetate based motion picture film when aged in contact with the various cans is shown in figures 7.41 - 7.45. The first point to note is that all the film acidity readings are comparable. However, a few features do come to light. Firstly the paper carton shows a better acidity trend compared to the metal can. This is due to the fact that the carton is absorbing any acid being produced as the cellulose acetate based film is degrading. Secondly the unstabilized cans, namely the Library of Congress can and the unstabilized HDPE Dancan show a decrease in pH. From this it can be assumed that the growth of hydroperoxide in the can has then had a detrimental effect of the consequent film stability. In contrast the acidity of the film within the stabilized Dancan has remained unaffected.
Chapter Eight.
Conclusions and Recommended Future Objectives.
Three types of containers were examined, vacuum sealed, metal
and plastic cans. It can be concluded that the alternative cans
offered no advantage over the traditional metal can in use. All
containers were shown to promote degradation by an oxidative route
and in the case of the metal container by catalyzing the decomposition
of active peroxides present in the film. On the other hand degradation
of the plastic containers induced higher levels of peroxide formation
in the film. Viscometric results therefore show film aged in plastic
cans to degrade more readily than in metal cans. The only can
comparable with metal can in the stabilized HDPE Dancan as seen
from viscosity graphs - otherwise plastic cans offer no real advantage
over metal cans.
Acidity measurements were not a reliable indicator of degradation
since some acid produced may be absorbed by the plastic can.
In light of these conclusions the following future objectives
can be made.
Furthermore work on FT-NMR and Molecular Modeling to correlate
chemical and physical property changes of the motion picture film
as it degrades could be undertaken. This then could be used to
identify critical points of breakdown in the film.
There is scope for further study on FT-NMR and Molecular Modeling
to help identify a better plasticizer system for cellulose acetate
based motion picture film.
The complexity of photographic gelatins may present a barrier
in order to obtain a more detailed understanding of emulsion breakdown.
To overcome this sample could be artificially aged where the initial
molecular weight distribution of the gelatin is known. One real
problem encountered with this particular study was the way the
motion picture film was artificially aged within the storage containers.
The films were placed in reels sandwiched between sheets of the
can studied. These were then placed in glass containers containing
potassium carbonate to obtain the 50% RH environment. This provides
a very basic environment which may have affected the way that
the film degraded. It is obviously very difficult to obtain an
artificial aging test which does not in some way differ from how
a film would naturally degrade. This is displayed in the differing
Arrehnius predictions obtained from artificial aging tests conducted
by different authors as described in section 4.7.1. Scope for
further work could include determining a standard method of artificial
aging that could then be adopted for studying the degradation
of the motion picture film.
Diana Michelle Williamson BSc(hons) GRSC. February 1994.
Ventilated Film Cans? - Food for Thought!
In the United States some archival storage cans are claimed to
be ventilated. The way it is done is by lifting the lid by means
of a few "points" in the button part.
Very good, but you have to consider that acetic acid vapors are
heavier than air and therefore have the tendency to "sink"
to a lower level. The vapors simply cannot get out of the can
fast enough. In a series of tests with measuring equipment from
Dräger the acidity was measured in cans with the lid lifted,
closed and with a 10mm hole close to the button. The level of
acidity was reduced by 50% in the version with the hole!
Spotting the "Vinegar Syndrome".
The easiest way is very simple: Smell it!. unless you have a cold!.
But when the acetic odor is apparent, chemical deterioration is
already quite advanced. Loss of the useful life of the film occurs
when shrinkage leads to massive failure of the bond between the
gelatin emulsion and the plastic base, causing creases and buckles
over the whole film surface. At the same time crystals of fire
retardant additives exude from plastic and form a disfiguring
"frost" on the surface. Extreme brittleness accompanies
these other problems. In cinema archives as well as still photographic
collections acetate degradation is much in evidence. So far, only
a small percentage of acetate film overall shows signs of advanced
deterioration. Acetate degrades with much less fanfare than nitrate,
but with equal finality.
You all know the smell when entering an archive and you can only
ask your staff to go through all cans to point out the sick ones
- that is a challenge to the human olfactory sense.
"Danchek" is a visible acid signal. The little device
(Patent 169.491) can be mounted to the side of any film can, like
a tiny warning lamp. Normally it's green. But when acid builds
up inside, Danchek turns from green to YELLOW.
Warning! It's that simple.
Bibliographic references.
(1) Archivum, Volume 2, No. 1. April 1992
Archivum Publishing, Box 140
3520 Farum, Denmark
(2) The Degradation of Cellulose Acetate Base Motion Picture
Film
Diana Michelle Williamson BSC(Hons) GRSC
A thesis submitted in partial fulfillment of the requirements
for the award of
Doctor of Philosophy, February 1994.
Department of Chemistry
Faculty of Science and Engineering
Manchester Metropolitan University
England.