Monthly Archives: August 2015

Recipe: Baking Mat Board

It is necessary to house select records below -5°C to slow the rate of degradation. When purchasing a freezer, ensure that it is frost-free and that there is a digital monitor on the exterior that supplies temperature and humidity readings.

Freezing Records, Emily Turgeon-Brunet

Freezing Records, Emily Turgeon-Brunet

To control the humidity of the freezer, it is important to use baked mat board when rehousing your records in preparation for freezing. Baking the pieces of mat board prior to use will thoroughly dry them out. The mat board should be baked in a standard convection oven for 3 – 5 minutes at 100°C. Ensure all areas of the mat board is exposed to the heat. Once it is removed from the oven, let it cool down and then use right away so that it does not begin to absorb moisture. It is recommended to sand the corners of the pieces of mat board so they do not puncture the bags.

For full instructions on freezing records, please see our guide, found in Preparing for Digitization, Temporary Housing:


McCormick-Goodhart, M. (2003, July 31). On the Cold Storage of Photographic Materials in a Conventional Freezer Using the Critical Moisture Indicator (CMI) Packaging Method. Retrieved July 21. 2015.

Bigelow, S. (2004, March). Cold Storage of Photographs at the City of Vancouver Archives. Retrieved July 21. 2015.

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Cellulose Nitrate Negatives

Throughout our travels we have come across a few archives that were unaware they had cellulose nitrate in their collection or that film based photographic material can be made of cellulose nitrate. Cellulose nitrate is flammable and releases hazardous nitrogen oxide gases as it deteriorates. It is extremely important to identify any cellulose nitrate in your holdings as this material is unstable and requires special storage and environmental considerations.


There are many ways to identify nitrate; however, few of the methods are absolute. It is beneficial to utilize a combination of methods to identify if a negative is nitrate:

  1. Edge printing: Many, but not all, manufacturers identified the type of film along one border of the film with nitrate or safety. Safety indicates the negative is acetate. It is important to note that some early nitrate does not have edge printing.
  2. Notch codes: A notch code is a group of indentations or recesses on the edge of a piece of film to help identify the film type and brand. If there is a ‘V’ notch code first from the edge of the negative, it is nitrate, and if there is a ‘U’ notch code first from the edge of the negatives, it is acetate. Notch codes are not always accurate as the photographer may have cut the film sheet for various reasons and removed the notch code closest to the edge.
    An example of edge printing and notch codes for a nitrate negative. Photo credit: Amanda Oliver

    An example of edge printing and notch codes for a nitrate negative. Photo credit: Amanda Oliver

    An example of edge printing and notch codes for an acetate negative. Photo credit: Amanda Oliver

    An example of edge printing and notch codes for an acetate negative. Photo credit: Amanda Oliver

  3. Dates of negatives: Kodak started selling cellulose nitrate negatives in 1889 and the last year of nitrate manufacture was 1950. These dates are only applicable for Kodak and there are no other dates for other manufacturers. Also, photographers may have purchased film and used it much later than the purchase date. The dates of the negatives are not always the most reliable method for identifying negatives.
  4. Level of deterioration: There are six levels of deterioration for nitrate negatives. The negatives start to yellow and mirror, then become sticky, then the image begins to fade before turning into a brownish powder. Please visit the NEDCC for images of all the different levels of deterioration:,-care,-and-duplication

    Example of nitrate deterioration level 2. Image is yellowing and beginning to mirror.  Photo credit: Amanda Oliver

    Example of nitrate deterioration level 2. Image is yellowing and beginning to mirror. Photo credit: Amanda Oliver

  5. Testing: There are a variety of tests available to identify nitrate; however, many of these tests are damaging to the negative. The diphenylamine, burn and float test can damage the record and should all be conducted by a professional. A non-destructive test is viewing the negative through a polarizer. Polyester negatives show red and green interference colours through a polarizer whereas nitrate and acetate do not. Please visit the NPS for more information about creating a polarizer:


If available, use duplicate access copies of the negatives. Allow material stored at cool temperatures to acclimatize before handling. Wear cotton or nitrile gloves when handling nitrate negatives. This prevents oil from transferring to the negatives and acts as a heat buffer. Negatives at a higher level of deterioration ignite at lower temperatures and body heat may trigger a reaction. Try to handle negatives by their edges and avoid touching the emulsion layer. Do not expose the negatives to any heat sources. If projecting or digitizing negatives, consider using a lower watt lightbulb in the projector or scanner.

Storage and Environment

It is important to isolate nitrate from other material is the collection. These negatives off-gas nitric oxide and nitrogen dioxide, which is harmful to humans and other items in the collection. For example, gases can cause skin and eye irritations as well as respiratory issues and cause paper to become discoloured and brittle and metal to corrode. Keep the storage space well ventilated.

Nitrate negatives should be housed in PAT approved negatives sleeves or envelopes and placed in an acid-free box. If freezing the negatives, the box should be sealed in a polypropylene bag. Freezing the negatives in a sealed bag counteracts the advice to keep the storage well ventilated; however, freezing is more beneficial to negatives in good condition than well ventilated storage.

Temperature and relative humidity levels are significant factors in slowing the deterioration of nitrate negatives. Cool to cold temperatures and 30-50% RH are recommended. If possible, store negatives in a cool – cold storage vault or freezer. Freezers must be frost-free and have the ability to monitor temperature and RH. Some freezer brands are also explosive-proof, which may be beneficial for these flammable records.


Consider digitizing the nitrate negatives prior to freezing them. Digitization prior to the start of or further deterioration ensures that an accurate representation of the record is being kept. It decreases use of the original, which prevents damage caused by handling. It also ensures the original is kept in a stable environment to prevent further degradation.

Disaster Preparedness

Due to the flammable nature of this material, it is important to include cellulose nitrate in your disaster plan. Train your staff on potential scenarios involving cellulose nitrate and advise your staff on its location within your collection. Set up a monitoring schedule to check for any signs of deterioration. Ensure that there are no heat sources, such as light bulbs or radiators, near this material. It is recommended to advise your local fire department where this material is located within your facility. This is extremely important as ignited cellulose nitrate creates its own oxygen and cannot be put out using water.

Disasters may also speed up the deterioration of nitrate negatives. While we have been helping archives across Alberta recover from the June 2013 floods, we have seen nitrate negatives’ deterioration accelerated due to their time in water. It is important to identify vulnerable media in your collection and plan for evacuations, if possible.


If you decide to dispose of the cellulose nitrate in your collection, be advised that it is considered a hazardous material. Check with Alberta Environmental Protection ( or with your local environmental agency for more information on safe disposal methods for nitrate film.


The Association of Moving Image Archivists. “Identifying and Handling Nitrate Film.” The Association of Moving Image Archivists December 2008. Accessed on April 2, 2015.

Fischer, Monique. “5.1 A Short Guide to Film Base Photographic Materials: Identification, Care and Duplication.” Northeast Document Conservation Centre. Accessed on April 2, 2015.,-care,-and-duplication

Kodak. “Storage and Handling of Processed Nitrate Film.” Kodak. Accessed on April 2, 2015.

Messier, Paul. “Preserving Your Collection of Film-Based Photographic Negatives.” Rocky Mountain Conservation Centre. Access on April 2, 2015.

National Park Service. “Cold Storage: A Long-Term Preservation Strategy for Film-Based Photographic Materials.” National Park Service. Accessed on April 2, 2015.

Reilly, James M. “IPI Storage Guide for Acetate Film.” Image Permanence Institute. Last modified 1996. Accessed on April 2, 2015.

Williams, R. Scott. “Display and Storage of Museum Objects Containing Cellulose Nitrate – CCI Notes 15/3.” Canadian Conservation Institute. Accessed April 2, 2015.

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Polyethylene Terephthalate (PET)

The science behind it

  • (C10H8O4)n
  • Melting point is around 250°C
  • Can be transparent or opaque white
  • It can be semi-rigid or rigid depending on how it was processed
  • It is a successful water and moisture barrier
  • A well-known commercial brand, produced in 1952 by Dupont™, is Mylar®

The story behind it

  • PET is a safe and stable plastic used often in conservation in the form of either foam or sheeting, to house or protect artifacts
  • It is also used during conservation treatment, e.g. for some humidification treatments, and as a barrier on the suction table
  • It is commonly used to make water bottles, and is a popular material in the art and drafting industry

We recommend PET as an important material for an emergency response or disaster kit. It can be draped over shelving units, tables, or boxes to protect records from water or moisture damage caused by sprinklers, or fire extinguishers.

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