Absolute Zero

The theoretical temperature at which materials have no thermal energy (and presumably would not deteriorate). Equal to -273.15° C. (-459.67° F.).

Acid-Free

Non-acidic material considered essential for the longevity of documents and their enclosures.

Acidic Alum rosin

Another name for aluminium sulphate, which has been used as a “sizing” agent in many machine-made papers from the 19th century to the present. The purpose of sizing is to strengthen the bonds between the paper’s fibres and to help prevent the migration of ink through the page. Alum rosin is a primary source of harmful acid in papers which have been sized with it.

Albumen Prints

The dominant form of photographic print from the mid-nineteenth century till approximately 1895. It gets its name from the egg whites (albumen) used to make the photographic paper. Albumens tend to be very thin papers with a glossy surface, and have a characteristic yellow or brownish yellow appearance.

Alkaline Buffer

Relative acidity or alkalinity of materials is measured by the potential hydrogen ion concentration using the pH scale. The pH scale ranges in value from 0 to 14, with a pH of 7.0 considered neutral, while values below 7.0 are increasingly acidic and above 7.0 increasingly alkaline. An alkaline buffer is a substance with a pH of over 7.0 that has been added to a material to neutralize harmful acids or to act as an alkaline reserve for the purpose of counteracting acids that may form in the future. The most common buffers used are magnesium carbonate or calcium carbonate.

Autocatalytic

A chemical reaction started by a substance (e.g. acid) that is not consumed by the reaction. The subsequent acids created by the chemical reaction then lead to further reactions in an ever-repetitive cycle. This type of chemical deterioration “feeds on itself”. In cellulose acetate film deterioration, acetic acid is the catalyst or substance that “feeds” the reaction.

Bookplates

A paper label with the owner’s name or other identifying information. It is pasted inside the cover of a book or on one of the first pages.

Calcium Carbonate

CaCO3, one of the most common buffering agents used to neutralize acids in paper and photographic materials.

Carbon Prints

Photographic prints using this process were made from the late 1860s to the 1940s. The name comes from the fact that carbon black was one of the first pigments used in this process, but many different colours are possible. The paper may be thick or thin, with a glossy or matte surface. Carbon prints have a subtle but distinctive “relief” appearance, when viewed under magnification, that makes the dark and light areas of the image seem to be of differing thickness.

Carriers

A clear plastic film or paper used to support (“carry”) an adhesive (e.g. mending tape) or photographic emulsion (e.g. 35mm negatives).

Cellulose Acetate

Cellulose acetate is a plastic that replaced cellulose nitrate as a base for photographic negatives and motion picture film. Early audio recordings, microfilm/microfiche and X-ray film also consisted of cellulose acetate. It is known as “safety film” because it is far less flammable than its predecessor (cellulose nitrate film). Cellulose acetate was introduced as early as 1909 but did not entirely replace cellulose nitrate until the 1950s. Its deterioration gives rise to the euphemistically named “vinegar syndrome” because of the characteristic odour of the acetic acid released as a by-product.

Cellulose Nitrate

An unstable early plastic formed by treating cellulose with a mixture of nitric and sulphuric acids. It was used extensively as a base for still and motion picture films in North America until the early 1950s but was discarded for this purpose because of its flammability and tendency to spontaneously combust.

Conservation

All acts requiring intervention to safeguard the future of an object. Conservation activities include examination, documentation, preservation, and various treatments. Conservation seeks to undertake the minimum amount of activity necessary to stabilize the object, whereas restoration seeks to make an object appear pristine and new.

Daguerreotype

Named after one of the pioneers of photography (Louis Daguerre, 1787-1851) this process was common from the early 1840s until approximately 1860. The photograph consists of a positive image on a highly polished silver surface, with a thin copper plate underneath. When viewed from different angles the image appears as either a positive or a negative.

Docket

A document format commonly used in the courts and government departments. It may consist of one or many pages, typically folded twice into three parts.

Document Box

A sturdy acid-free cardboard box with a hinged lid. It is used widely in archives and comes is two standard sizes: letter, 12 x 5 x 10" (0.35 cubic foot); and legal size 15 x 5 x 10" (0.45 cubic foot).

Friable

Anything that is easily crumbled or broken into small fragments, usually with light hand pressure.

Full-Coat Magnetic Film

Full-Coat magnetic film has the magnetic-coating compound applied across the film from edge to edge.

Inherent Vice

A term used by conservators to describe any characteristics of an object that were present at its creation and that lead to accelerated deterioration. A common example is the acidity present in cheaper papers such as newsprint; this increases the speed with which paper will discolour and become brittle.

Japanese Paper

Any one of a host of papers traditionally made in Japan. Conservators often favour the use of good quality Japanese papers with long durable fibres and chemical stability in paper repair.

Lantern Slide

An early form of projector slide used with a “magic lantern” to project images on a wall or screen. Originally, images were painted by hand on pieces of glass but by the mid-19th century photographic images were commonly used on either a glass or plastic support.

Leader

A short length of protective film at the beginning of a roll of movie film.

Marginalia

Any additional handwritten text alongside the printed or hand-written body of a page.

Mat Burn

Staining of an object by components migrating from the edge of a poor quality mat board (especially the window). Mat burn is usually reddish-brown in colour and can be very disfiguring when the mat is removed.

Photographic Activity Test (PAT)

One of several tests used to determine if a material is safe to use for storing photographs.

Platinum Prints

These were common from 1880 until the 1930s and were also known as platinotypes. They have a matte surface and are of a black or slightly blue-black colour. Platinum prints used metallic platinum rather than the more-common silver and had a reputation for being able to reproduce delicate distinctions in tone. They are a very stable, enduring format.

Polypropylene

A plastic often used in museums and archives because it is chemically stable and non-acidic. It is often found under the trade names Coroplast and Microfoam, and is recommended for products such as film cans.

PVC (polyvinyl chloride)

A type of plastic considered unsuitable for use as a storage material in archives and museums because it emits harmful compounds such as acids as it ages.

Preservation

Any effort to extend the lifespan of an object by improving the methods used to care for it. This includes safe handling, security, storage, and environmental conditions.

Relative Humidity (RH)

The amount of water vapour in a volume of air expressed as a percentage of the total water the air can hold at that same temperature. For most archival purposes a stable RH of 40-50% is desired.

Salted Paper Prints

A common format of photographic print from 1840 to about 1855. Ordinary writing paper was sensitized with sodium chloride (salt) and a silver halide compound. The image is most commonly a reddish brown, purple, or yellow-brown.

Silver Gelatin Prints

The first silver gelatin prints appeared in the late 1880s. They were the dominant print medium from about 1905 until the 1960s, when colour photography took over, although they are still in use. They can have glossy or matte finishes. More contemporary prints can be reliably distinguished from other photographic media only under microscopic examination (which reveals the fact that the paper fibres are almost totally hidden by a special coating to make the paper appear whiter).

Spoking

The radial pattern that becomes visible when a reel of film has not been wound and stored properly. Over time it may become a permanent feature of the film and result in irreversible damage.

Textblock

The main body of a book containing all the pages with printed words and images. It does not include any of the papers added by the bookbinder, such as the coloured endpapers and covers.

Tintype

This type of photograph appeared in the late 1850s and was made well into the 20th century. It is also known by its more accurate name of ferrotype because the image is adhered to a thin sheet of lacquered iron. This makes tintypes easy to identify because a magnet will stick to the back of the photograph (never try this test on the image side).

Vinegar Syndrome

A term used to describe the autocatalytic deterioration of cellulose acetate. Acetic acid is released as a by-product of deterioration and typically smells like vinegar.

Wax Cylinder

One of the earliest formats for making sound recordings. This was invented by Thomas Edison in the late 1880s and used until the early 20th century. This format used a recorder to carve a groove into a rotating tube of softened wax with a needle that was vibrating from the sound pressure collected at the small end of a trumpet-like device. Each cylinder could hold between two and four minutes of sound recording, depending on the recording speed. These cylinders are very fragile.

Wheat-Starch Paste

An adhesive made by mixing and cooking water and an extremely pure form of wheat starch. It is used in paper repair by conservators because it makes relatively strong bonds but is easily removed with moisture or humidity, and does not discolour or deteriorate over time.

Sources

• Care and Identification of 19th-Century Photographic Prints, James M. Reilly; Eastman Kodak, 1986.

• Caring for Collections Across Australia – Glossary, viewed 17 June 2003.

• Code of Ethics and Guidance for Practice, Third Edition. Canadian Association for Conservation of Cultural Property and the Canadian Association of Professional Conservators, 2000.

• History and Properties of Film Supports, Peter Z. Adelstein, Proceedings of the International Symposium: Conservation in Archives, May 10-12, 1988.
  
• IPI Storage Guide for Acetate Film, James M. Reilly, Image Permanence Institute, 1996.
  
• Preserving Archives and Manuscripts, Mary Lynn Ritzenthaler, Society of American Archivists, 1993. plus several dictionaries.