The preservation of photographic negatives at home
One of the most important aspects of being an archivist is to ensure the long term preservation and accessibility of archival material. On a day to day basis we monitor the environmental conditions where materials are stored, we rehouse documents into archival quality enclosures, we remove things which could cause damage to material such as rusty pins or staples and we implement digitisation programmes for fragile materials so that the originals can be preserved.
In the case of photographic material there are a number of factors that influence its long term preservation including the environment in which the material is being stored and the the type of enclosure that it is housed in. Many of the methods that we employ within the archive to preserve our material can also be applied at home to ensure that our personal photographic collections can be preserved for the future. In this post I would like to provide some practical advice for the preservation of photographic negatives at home, whether that encompasses historic family collections or your current negatives that you are shooting today.
The gloves are….on.
A regular source of consternation for archivists is the perception in the media that archival material must be handled while wearing white cotton gloves. In actual fact, wearing gloves can cause damage to paper documents rather than prevent it as you have less dexterity while wearing gloves. This means that you could accidentally tear a page and because cotton gloves get dirty they could transfer dirt to a document.
However, there are always exceptions to the rule and photographic materials are definitely the exception! Oils and dirt from your fingerprints can damage photographic materials and cause permanent staining or etching in the gelatin emulsion. For this reason it is very important to wear a pair of clean un-powdered nitrile or latex gloves while handling negatives. If you do not have any gloves then make sure your hands are clean and dry and only hold negatives by the edges to avoid fingerprints on the images.
Identifying your negatives
One of the most critical factors in ensuring the survival of photographic negatives is determining the material that they are made from. If you find yourself dealing with negatives that have been in your family for a few generations you may potentially have some cellulose nitrate or cellulose acetate film in your possession. These film bases are chemically unstable and even hazardous and as such, it is vitally important to identify what film stock you have so that you can preserve it accordingly. It is also important to note that cellulose acetate is still in use as a film base and so even the modern day film photographer should be striving to preserve your current negatives in the best possible conditions to avoid future degradation. Have a look at the technical specifications of your preferred film brand to see if your current film stock is acetate or polyester. Polyester based negatives are chemically stable and present less of an issue in terms of degradation.
Note: When working with your photographic negatives make sure that you are working in a well ventilated space, especially if you suspect that you have nitrate or acetate film stock that is degrading. The by-products of this degradation can be harmful to health. This is also the case if you find that your negatives have mould on them. Take the affected negatives and seal them in a plastic bag. The Canadian Conservation Institute offers excellent advice on dealing with mould.
Cellulose Nitrate
The first cellulose nitrate negatives were sold by Eastman Kodak in 1889 ushering in a new era in film photography. This new flexible film was more convenient for professional photographers and also helped to open photography to the amateur market. Nitrate film continued to be used right up until the early 1950’s for negatives, transparencies, x-rays and motion picture film. The problem with cellulose nitrate is that it was and is highly flammable and can have a low temperature of ignition of 38 degrees celsius as it degrades. When nitrate film starts to burn it will continue to do so until it is consumed which is what can make it so dangerous when stored in large quantities. It also releases hazardous gasses as it deteriorates.
If you have any film in your collection which you believe may date from 1890-1950 then it may contain some nitrate film and you should separate it from other negatives.
Silver mirroring on a nitrate negative. Image from the NEDCC.
One way in which you can identify whether your film is nitrate, is by looking for signs of deterioration. One of the first signs of deterioration is yellowing of the film and silver mirroring which presents as a bluish metallic deposit or sheen on the film. As cellulose nitrate begins to deteriorate it releases nitric oxide, nitrous oxide and nitrous dioxide and these gasses when combined with water, form nitric acid. The nitric acid then further degrades the film which will have a strong noxious odour and the film becomes sticky. As deterioration continues the film will become an amber colour and start to fade. It will then become soft before finally breaking down completely and turning into a brown acid powder.
Yellowing of a nitrate negative. Image from Preservation Self Assessment Program.
Another way in which you can identify your negatives is by looking at the edge printing on the film. Some manufacturers printed the words nitrate or safety on the edge of the film, however this was not done on early nitrate negatives. You can also look for notch codes on the film. A ‘V’ notch code (first notch from the edge) will identify pre-1949 Kodak film as nitrate. A ‘U’ shaped notch will indicate that the film is acetate.
Nitrate edge markings. Image from Library and Archives Canada.
Nitrate ‘V’ notch code. Image from NEDCC.
Dating the film is another way in which you may be able to ascertain whether it is nitrate. Eastman Kodak are the only manufacturer to have provided dates on their nitrate film production so this is helpful if the negatives are Kodak but not so helpful if they are from another manufacturer. Kodak stopped manufacturing 35mm roll films in nitrate in 1938, roll films in 616, 620 etc. in 1950 and portrait and commercial sheet films in 1939.
The NEDCC provides information on testing film to determine whether it is nitrate or acetate. Some of these testing methods are potentially dangerous and should not be carried out by untrained individuals. If you are unable to determine what type of film stock you have in your possession, then please consult a professional before trying to test the negatives yourself. Contact an archive for advice or seek out a company with specialist expertise in photographic conservation.
Cellulose Acetate
Cellulose acetate is also known as ‘safety’ film but despite this name it is a chemically unstable film base that was in use from the mid 1920’s. Many forms of this film base were introduced through the twentieth century including cellulose diacetate, cellulose acetate propionate and cellulose acetate butyrate. However, the need for a film base with improved properties led to the development of cellulose triacetate in the mid 1940’s. And while polyester film became more widely used from the 1960’s, cellulose triacetate continues to be used as a film base today by many companies including Kodak and Ilford.
If cellulose acetate based film is stored at high heat and humidity it begins to deteriorate and becomes acidic. It also becomes brittle, begins to shrink and gives off acetic acid. This acetic acid produces a vinegary odour causing what has become known as ‘vinegar syndrome’. This vinegar odour and the shrinking of the film are two of the main ways in which you will be able to identify whether you have acetate based film in your collection. Deterioration of cellulose acetate also causes the formation of bubbles and crystals in the film and in severe cases, channeling in the film.
Channeling in an acetate negative. Image from the Preservation Self Assessment Program.
A visual guide to the stages of deterioration of acetate film can be seen clearly here.
As is the case with cellulose nitrate, another way to identify acetate film is through the edge printing. Some acetate film will have the word safety printed in the border. It may also have the manufacturer name or the U shaped notch code that was mentioned earlier. If you believe your negatives were produced after 1955, they will be either acetate or polyester.
Acetate edge markings. Image from Library and Archives Canada.
Acetate ‘U’ notch code from NEDCC.
If you suspect that you have nitrate or acetate based film in your family collection then please separate it from all other photographic material as it can cause deterioration of other material that it comes into contact with. As stated above, contact a professional who can then advise you how best to proceed.
Storing your negatives: Environment
The deterioration of both nitrate and acetate films is linked to the storage conditions in which they are kept. High temperature and humidity is what causes these negatives to degrade and so managing the temperature and the relative humidity is key to their preservation. In an archival setting it is recommended that nitrate and acetate film types be stored in cold or subzero conditions with a relative humidity of 30-50% which will help to slow down the process of deterioration. Black and white negatives from the 1980’s onwards can be kept at a temperature between 8-16 degrees celsius and a relative humidity of 30-50% while early colour film is also best stored in cold or sub zero conditions. Almost all photographic materials will benefit from being kept in cold storage.
In a personal home setting you may be unable to freeze your negatives or achieve optimum temperature and relative humidity levels but if you determine that you have nitrate or older acetate negatives then try to keep them in cold storage if possible and seek out professional advice. Store your polyester negatives in cool, dry conditions with good air circulation and away from light. Attics and basements are not recommended for storage of photographic material due to poor air circulation and the potential for damp. Also avoid storing your material near a water or heat source and try to keep it a reasonable distance off the ground in case of flooding. Assessing potential hazards is crucial for giving your material the best chance of survival. This can be said for any important family archival material and not just photographic items.
Storing your negatives: Enclosures
One of the most important things you can do for the preservation of photographic negatives at home is to ensure that your negatives are stored in appropriate enclosures. Photographic negatives should be stored in negative sleeves. For cellulose nitrate and acetate it is recommended that you use archival buffered paper sleeves. This is because paper will absorb the acidic by-products of deterioration while plastic enclosures can restrict the migration of acids.
For the storage of polyester or recently produced acetate negatives, the sleeves should be made from archival quality polyester, polypropylene, or polyethylene. Polyester is the best choice as it is the most inert, this is what I would use in my job and the product is called mylar or melinex. There are a number of good quality products on the market at reasonable prices which will allow you to store your negatives properly at home. Choose products that are PH neutral, acid-free and lignin-free as modern paper contains lignin which produces harmful acids as it degrades.
My own negatives stored in archival quality sleeves.
Look for products that have passed the Photographic Activity Test (PAT). This test was devised by the Image Permanence Institute and is an international standard ISO 18916. It was designed to evaluate photographic display and storage products to determine their suitability for the storage of photographic materials. In Ireland you can purchase Clear File archival storage sleeves at a reasonable price from The Photoshop. Clear File state on their website that they have passed the PAT test.
A note on glassine: While you can purchase glassine sleeves for negatives that are stated to be archival, they are best avoided as they can still become acidic over time. They can also become soft and stick to photographic emulsions if stored at high humidity levels.
A second layer of protection is to place your negative sleeves into an acid-free archival box or binder where they will not be not be susceptible to dust or light damage and place these on a metal shelf or in a cabinet.
An example of an archival quality ringbinder box from Preservation Equipment Ltd.
My own personal preservation measures include storing my negatives in archival quality sleeves. These sleeves are stored in a binder and kept in a cabinet away from light sources, heat sources and away from anywhere that would be prone to damp.
To infinity and beyond….
Ok, so your material may not last for infinity but you want to give it the best possible chance. It would be remiss of me not to mention digitisation as another potential method for preserving your images. If you have negatives that are showing signs of deterioration, then you can digitise them using a scanner or digital camera set up. Please be aware that your digitised material will also require its own digital preservation to ensure long term accessibility. The risk of obsolescence or media failure are some of the major threats to digital material and so digitisation alone is not a one stop solution. Your digital images will require active management throughout their lifespan.
To begin with, save your digitised images in a lossless format such as .TIFF and name the images in a logical consistent manner. Save copies of your images to several different storage media such as an external hard-drive and cloud storage. Be aware that the lifespan of an external hard drive is estimated to be approximately 5 years, so it is good practice to regularly migrate your images to new storage media.
In summary
Task 1: Identify what you have in your personal collection. Are the film bases nitrate, acetate or polyester?
Task 2: Speak to an archival or photographic expert if you discover that your film is acetate or nitrate. For now, separate it from any other material and keep it in cool conditions.
Task 3: Purchase archival quality, PAT tested enclosures to rehouse your negatives. Keep your sleeves in a box or binder to avoid dust and light. Make sure any enclosures you use are acid-free and lignin-free.
Task 4: Assess your environment for any potential environmental hazards. Choose a shelf or cabinet away from heat, water and light to store your box of negatives.
Task 5: Assess whether digitisation is required for negatives that are deteriorating and if so, plan how you will manage the digital files over time.
Ultimately, you want to give your negatives the best possible chance of survival and so investing in good quality enclosures, storing them appropriately and assessing the environmental conditions will go a long way towards ensuring the longevity of your material.
If you have any questions related to this post then please do not hesitate to get in touch and I will endeavour to help to the best of my ability. As a trained archivist I can advise on the preservation methods I would use in my day to day work. For serious cases of deteriorated material, the advice of a trained conservator or specialist should be sought.
Sources
BS 4971:2017 Conservation and care of archive and library collections.
North East Document Conservation Centre: Photographic Preservation Leaflets
British Library Preservation Advisory Centre: Preservation of Photographic Material
Library of Congress: Care, Handling and Storage of Photographs
Carter, E.A., Swarbrick, B., Harrison, T.M. et al. Rapid identification of cellulose nitrate and cellulose acetate film in historic photograph collections. Herit Sci8, 51 (2020). https://doi.org/10.1186/s40494-020-00395-y
Silva, Joanna., Roldão, Élia., Ramos, Ana. et al. “Conservation of Cellulose Acetate Photographic Negatives: Searching for New Approaches” in CoMa 2013 : Safeguarding Image Collections, edited by Arijs, Hilke, Newcastle-upon-Tyne: Cambridge Scholars Publisher, 2014.