Preservation of 20th Century Photographic Materials
Cheryl Jackson
Photo Conservator
National Archives of Australia
1. Good afternoon everyone, thanks for coming along to this session. This afternoon I’m going to be
talking about the nature of the modern photographic materials we hold at the National Archives of
Australia. The preservation needs of any archival material can be met more
successfully if the materials themselves are better understood. Photographic
materials are often more complex than we realise. We all have so many
photos of our own, and such a huge capacity for taking photos these days, we
often tend to look on these materials as everyday, disposable items rather
than fragile, unique ones. I will be introducing you to the materials found in
black and white negatives, black and white prints, colour prints and digital
colour prints, and what we do, at the National Archives of Australia towards
preserving these materials. This presentation will, hopefully, make you more
familiar with these materials, and help you understand why they require high preservation
standards.
I will say now that this presentation includes an image of an Indigenous Australians who would
now be deceased
2.The Canberra repository of the National Archives of Australia houses over 1 million photographic
images listed and described as photographs. In addition to this, there are over 1 million Service and
Immigration documents which contain a passport size identity photograph and/or an original
negative. This means that in the Canberra office alone we have, at a conservative estimate, 2 million
images requiring preservation. In Canberra we hold less than a third of the total holdings of the
National Archives, so the estimate for the total archive probably approaches 6 million photographs.
3. These materials range from a 3.5m long albumen panorama to
4. 35mm contact prints and their associated negatives
5. Paget plates taken in Antarctica
6. and modern colour prints and their negatives.
7. “Black and White” photographs actually come in a variety of forms. They
may have different supports.
-
Metal – daguerreotype, tintype.
Glass – Ambrotypes, negatives, lantern slides.
Paper – collodion silver, gelatine silver,
cyanotypes.
8. Different binder layers.
-
Gelatine– from animal hides and skins
Albumen – from eggs
Collodion – nitrated cellulose
None – image forming material absorbed into paper fibres
9. Or different image forming materials
- Metals – Silver, Iron, Platinum
Pigment – Carbon Prints, Collotypes, Inkjet
10. But by far the most common black and white materials in 20thC collections are
silver gelatine prints and negatives.
11. Black and white negatives are our biggest photographic challenge
at the National Archives of Australia at the moment.
12. We have conquered glass plates.
13. We have them in photo safe enclosures in a
storage format that was tested by dropping a
-
dummy box from a 2 storey stair well, and not one of the dummy glass plates broke.
All the storage materials we use for photographic items have been tested against the photographic
Activity Test. This is a test developed by the Image Permanence Institute in Rochester, NY to see if
packaging materials harm either the silver of an image or stain the paper support. Samples are
sandwiched with test strips of colloidal silver film, and processed photographic paper and incubated
at an elevated temperature and humidity level for 15 days. The samples are then assessed to see if
they caused damage to the detector strips or not. Only material that passes the test is used at the
National Archives. The National Archives is the only accredited testing facility carrying out the PAT in
Australia.
14. The plates that come in to us already broken are individually
housed and stored flat in the cold room.
15. And we have the professional expertise on staff to deal with
highly fragile materials.
16. Cellulose nitrate negatives on paper files are a particular concern for us
at the moment.
17. As nitrate film deteriorates it releases highly reactive nitro groups which
combine with moisture and other gases in the atmosphere to
produce highly acidic compounds. These acids will cause
adjacent archival materials to deteriorate rapidly. They will
attack the cellulose chain and cause it to break apart, they will
attack the protein molecules that make up the gelatine layer,
causing it to become soft and sticky and they will attack the
silver image material causing it to lose density.
18. Accompanying photos and documents will become extremely brittle, and to save these items,
the negative needs to be separated from the files. Unfortunately,
with a million plus files, this is a huge task.
19. The negatives are being separated where they are obviously
damaging the file, as the files are being digitised or described. The
deteriorated negatives are digitised along with the rest of the file,
even though there is no useful information left on them. They are
done so that users of the digital file can be confident no part of the file has been left out.
20. As well as nitrate negatives, we have thousands of cellulose acetate negatives. In 2005, we
conducted a Vinegar Syndrome survey in the acetate material using Acid Detection Strips from the
Image Permanence Institute in Rochester, NY. Hot spots identified by that survey were prioritised for
digitisation. The two highest priority levels have been digitised and the third level is ongoing at the
moment. It should be pointed out here that acetate material that is completely deteriorated and
channelled will not return a positive AD strip result. This is because all the acetic acid that was being
released by the film has gone, and the film has already
reached a severely deteriorated state.
21. In this representation of a cellulose acetate molecule,
you can see the acetyl groups which can break off the side
of the cellulose chain. Film that does not return a positive
response to an AD strip has lost these side groups already.
22. During the survey, particular brands of negatives
were found to deteriorate more readily, as were
particular notch codes. Notch codes are applied to sheet
negatives by the manufacturer to indicate the film type.
“U” notched material has regularly been found in the
National Archives to be deteriorating. It is not clear
which manufacturer produced these negatives, as more
than one has used this notch code.
23. This acetate negative, you can see, has a U notch
code, and is actively deteriorating. The base has
begun to shrink causing the gelatine layer to start to
channel. You can also see that the acetate has
developed a blue colour cast. This is caused when
the antihalation dyes in the film base revert back to
their original colour as the pH of the plastic changes
to a more acidic state. These dyes may also form a
pink cast. There is little that can be done for a
negative once it has reached this point. Extremely
valuable negatives can be treated to lift and remove
the gelatine layer and transfer it onto a new sheet of film, but this is an extremely difficult process
and requires a highly skilled operator. This negative was digitised and moved into frozen storage.
Time Line of Photographic Film Bases
24. Fortunately, nitrate and acetate materials were
replaced in the 1940’s and 50’s with cellulose
triacetate film and polyester film. Cellulose triacetate
is more stable than earlier cellulose acetate materials,
but it will still degrade over time. Polyester film has
proved to be the most stable – so far.
Film type
1880
Nitrate Sheet Film
Nitrate Roll Film
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
----------------------------------------------------------------]
--------------------------------------------------------------]
Diacetate Sheet film
Diacetate Roll Film
Cellulose Acetate Propionate Sheet Film
Cellulose Acetate Propionate Roll Film
Cellulose Acetate Butyrate Sheet Film
Cellulose Acetate Butyrate Roll Film
---------------------]
---------------]
-------------------]
-------------------]
----------------------------------------------------------]
B&W Triacetate Sheet Film
B&W Triacetate Roll Film
--------------------------------------------------
-------------------------------------------------
B&W Polyester Sheet Film
B&W Polyester Roll Film
-----------------------------------
-----------------------------------
--------------- denotes unstable materials
25. Black and white print materials appear in all sorts of series in the
National Archives, and are always a pleasure to find.
These images dates from1897 and are included in a very early Copyright
series, C2229. They don’t really fit into the topic of this talk, but they are too
beautiful to ignore.
26. Modern silver gelatine print materials are composed of a
support layer, a baryta layer, a gelatine layer and silver as the
image forming material.
27. Prints made prior to the 1960’s will have
- a good quality paper base (it had to be good paper to avoid
damaging the silver),
- a baryta layer (which is barium sulphate in gelatine) to
smooth out the paper surface and provide a bright white
background for the image,
- the gelatine layer (which is around 6 micrometres thick)(
- and the silver image material (these clumps of silver are
around half a micrometre in size).
28. Modern B&W papers and negatives use filamentary silver
as their image forming material. The appearance of
photographic silver is a direct result of the size and shape of
the silver grains. The complex structure of the grains absorbs
light evenly across the visible light spectrum giving the silver
a black appearance. Such finely divided silver is, of course,
highly vulnerable to deterioration, and it is only the
enveloping gelatine layer that saves the silver from immediate damage.
If the humidity in the storage area is allowed to rise, the gelatine layer will swell with the extra
moisture and allow both the migration of unreacted silver through the gelatine, and the ingress of
atmospheric pollutants. These pollutants may come from the environment or from poor quality
enclosure materials.
29. The damage may appear as silver mirroring or yellowing of the
silver. In the past, yellowed silver may have been bleached and
redeveloped to reproduce a strong black and white image BUT this can
have unpredictable results and can change the nature of the
photograph permanently. It is no longer practised as a standard
treatment.
Removing the silver mirroring is also losing favour among photographic conservators as it is original
image material that is being irreversibly removed from the photograph.
30. Unfortunately, silver mirroring can also hide detail in the maximum
density areas of the image, and if the item is being duplicated, that detail is
required. This is when a decision has to be made between conservators and
other stakeholders as to whether the silver mirroring should be removed or
not.
31. If the decision is made to remove the silver mirroring at the National
Archives, the item undergoes intensive treatment with full
documentation (including before and after treatment photos) and the
silver mirroring is removed by hand. Chemical conversion treatments
are not used.
32. The damage to the silver may also be localised rather than
general. Here are two examples of beautiful fingerprints left
behind by careless handlers. Fingerprints not only cause the
silver to tarnish, but they also etch the gelatine layer and
provide areas of disruption which mould spores may colonise.
And when we remember that the gelatine layer may only be 6
micrometres thick, there is not a lot there to withstand any
kind of damage.
33. Light, moisture and insects can have dire effects on
photographic materials. Here we see the effects of all three
combined – fly specs have caused softening of the gelatine
layer thru moisture and enzyme attack, which has then
become more vulnerable to damage from elevated
humidity levels (here in Queensland) and UV light. The affected gelatine has crumbled away leaving
the baryta layer exposed. Nothing can be done to reverse this damage. The item can be treated and
stabilised in this condition, and cosmetically improved if required, but the gelatine has been lost and
the damage cannot be undone.
34. At the National Archives of Australia we routinely carry
out conservation treatments on photographic material. These
treatments include: surface cleaning
35. Adhesive tape removal
36. Backing removals – in fact I’m just about to embark on a project to
establish a faster, more efficient method of removing dry mount tissues
from photographic materials. This research will, hopefully, be presented
at the Joint AIC-ICOM-CC meeting in Wellington, NZ in February 2013.
37. washing, including capillary, immersion and float washing
38. humidification and flattening.
39. During the 1970’s Resin Coated paper was introduced. This material has a polyethylene layer
applied to the front and the back of the paper to make it virtually waterproof. The gelatine binder
layer and silver image are still present, but the
baryta layer is replaced by a pigmented
polyethylene layer on top of the paper. There is
a second, clear PE layer on the back of the
paper. These waterproof layers enabled much
faster processing time, which in turn enabled
automated processing. The faster processing
times unfortunately meant that the binder layer was not always cleared as well as it should be and
residual processing chemicals caused the silver to deteriorate quite quickly.
40. These prints presented their own problems in their early days – light
caused the pigmented PE layer to crack all over, causing irreversible
damage. This problem was later rectified by the addition of an
antioxidant in the PE layer.
41. Colour photographs come in different forms too – early additive
colour, silver dye-bleach prints, dye sublimation, instant colour, and by
far the most common, chromogenic colour.
42. This colour system covers colour transparencies, negatives and
prints.
43. Early prints were on good quality paper, with a baryta layer, and
a gelatine layer, but this time, the gelatine contains a complex
system of dyes and filters all in the one tiny image forming layer.
44. Before the print or film is processed, the image layers also
contain silver halides. The silver halide is reduced to silver metal
which activates the dyes. The silver is then bleached out leaving a
pure colour image.
45. A colour film can have more than 9 different layers in the
emulsion. Each individual dye layer can have three separate sublayers. And this whole binder is still only micrometers thick.
46. The primary concern with chromogenic colour material is
dye shift. This is where one dye will fade faster than the
other two. Here we see an image where the cyan dye has
faded, leaving a magenta/yellow colour cast. These days, of
course this can be corrected with the click of a computer
button (click) but this does not help the original item. This
print needs cold storage to slow down the existing
deterioration. In response to this fading, chromogenic colour prints became more and more stable,
particularly in the 1980’s.
47. This dye fade is caused by the complex organic dye molecule
changing shape and therefore reflecting light differently. The colour
of anything is a function of how light is absorbed or reflected by it.
The structure of a magenta dye molecule causes it to reflect
magenta light back to us. If the shape of the dye molecule changes,
it won’t reflect light back in the same way, changing the colour we
see. Chromogenic prints are particularly susceptible to this
deterioration as the dyes start as two separate colourless molecules
(a colour coupler and an oxidised developer) which are then joined
together in the developing bath to form a coloured dye. These dyes
always want to revert to their more stable colourless state, splitting
apart and losing colour. This reaction is accelerated by warm
temperatures, so cold storage is a must.
48. Colour couplers which are not properly washed out of a print can cause
another problem among early colour prints. Even in dark storage these
residual colour couplers can form a strong overall yellow stain. Currently,
this deterioration is not reversible and can only be slowed down by placing
the item in cold storage.
49. Modern colour materials are also made on resin coated papers with a similar structure to B&W
RC paper. The earliest colour RC materials are also prone to
cracking, as illustrated before.
50. RC papers have the added problem of being difficult to repair
if they get torn. The resin coating will stretch along the tear, and a
method of reintegrating the resin coating is yet to be developed.
51. These modern RC papers are the ones still being used in digital
exposure of chromogenic prints. The dye systems are much the
same as in light exposed prints, but they are exposed via lasers or
LEDs, giving the prints a very slight linear appearance under magnification:
52. Because these types of digital prints have much the same dye
sets as light exposed chromogenic prints, they should be stored in
the same environmental conditions as light exposed chromogenic
prints.
53. As newer materials start coming into the Archives, we need to
become aware of their properties as well. Inkjet photo prints will
become more prominent in transfers in the future, and although
they are actually just ink on paper, they are considered
photographs, and photo conservators will be asked to advise on
them. Once again, they require the same storage and display
conditions as chromogenic colour prints.
54. The dye images will be vulnerable to light fading and
temperature induced deterioration, particularly if the inks
and the papers are not matched. In these prints, the same ink
and the same printer were used on the same day, but one
paper matched the ink set and the other was a generic paper
from the supermarket. They were both displayed side by side
on my refrigerator for a period of only a couple of months.
55. The papers will require consideration as well as the images
as they too are complex constructions with multiple layers of
PE, paper, receiving layers, filtering layers, anti-blocking layers
and anticurl layers. This technology is constantly changing and
is closely guarded by the manufacturers, so at the moment we
only have accelerated aging tests to go on,
56. Plus anecdotal evidence of our own poorly made prints at
home.
57. Luckily, at the Archives national office in
Canberra, we have a purpose built repository
designed with preservation in mind.
Our building is a massive concrete structure
designed for maximum thermal mass, and little
ingress of natural light. The windows face south
(which in the Southern Hemisphere is away
from the sun) and are double glazed to reduce
thermal loss. It is built on a raised earth
platform to avoid flood risks. Inside the building
are the usual features of sprinklers, fire doors, environmental control, air filtering, secure entry and
electronically controlled records to reduce the risk of damage or loss.
58. Within this building we have one room set aside which
operates at cool temperatures. At the time the Mitchell
building was constructed, (over 30 years ago) no cool room
was included as the storage standard for photographic
materials was not fixed in place. Around 5 years after the
building was constructed, the need for cooler storage
temperatures for photographic material was realised, and
the “Cold Room” as we know it was established in one of the
existing storage spaces. The air handling units for this room were set at 10 degrees C and 35% RH,
which were the recommended storage conditions for photographic media at that time.
59. The advantages of cooler temperatures for black and white
film are in slowing the deterioration of the film base. It does not
have a major effect on image stability. For colour material,
however, the advantages are two fold – the film base will be
more stable, and the colour dyes will be more stable as well.
The degradation of cellulose acetate and nitrate plastics is
significantly slowed if the storage temperature is decreased.
60. This room remains at these conditions today, even though the storage
standard has changed, as it is now a mixed media store. So, it now stores
photographic negatives, colour prints and some black and white prints but
also a large range of glass plate material and a limited amount of magnetic
media, which governs how low the temperature can go. Magnetic media
should not be stored below 10 C to avoid damaging the lubricant layers in
the tape.
61. After a vinegar syndrome survey was done of the negatives in
the Cold Room, and some material was found to be approaching
the autocatalytic point in its degradation cycle, and as we could
not reduce the temperature in the whole storage area, freezers
were purchased to house the most at-risk material in an effort to
reduce its on-going deterioration as much as possible. Negatives
requiring storage in the freezers were (are) digitised, then
vacuum sealed in tri-layer envelopes
62. These freezers run at -20 C which is the recommended temperature for
maximum longevity of colour photographic materials. This is not a
temperature we have set, but rather what this model of freezer runs at by
default, which is convenient.
63. Fortunately, we are now in the very
early planning stages for a new storage
and preservation facility in Canberra and
our colleagues in the Archives Sydney
office are conducting research into
options for specialised storage.
In our new facility we are hoping to have
subzero, cold and cool storage areas to
better cater for the needs of our unique and irreplaceable photographic archives.
64. Thankyou
BIBLIOGRAPHY
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http://www.paulmessier.com/pm/papers.html
http://www.graphicsatlas.org/
Coote, J, 1993, The Illustrated History of Colour Photography, Fountain Press, p161
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Cheryl Jackson
Photo Conservator
National Archives of Australia
Cheryl.jackson@naa.gov.au