Tech tip3 min read
Document and Photograph Preservation Dictionary
Plain-language glossary of common terms in the preservation and storage of photographs, microfilm and archival materials.
This glossary explains, in plain language, terms commonly used in the preservation and storage of photographs, microfilm and archival materials.
Highlights
- Acidic materials, lignin, flexible PVC and glassine are not suitable for contact with photographs
- Polyester and polypropylene are considered safe by ISO but must pass the PAT
- ISO recommends 30% to 50% relative humidity for storage
- Reducing UV exposure extends image life
Terms
| Term | Definition |
|---|---|
| Acids | Substances that produce a hydrogen ion concentration above 10-7 in water and can shorten the life of photographs and enclosures |
| Adhesive | A substance that bonds two or more materials together (such as pressure-sensitive or liquid adhesive) |
| Alkali / Base | Substances with a hydrogen ion concentration below 10-7; in paper, also used to mean the presence of an alkaline buffer |
| Archival | A term for a product's stability over time that has no standard definition or quantitative test method |
| Bleed-through | Transfer of color from one side of a material to the other |
| Digital image | Any image stored as numerical values on optical or magnetic media |
| Fading | Gradual loss of color caused by breakdown of colorants |
| Gelatin stain | Yellowing or browning of the gelatin layer in black-and-white or color photographs |
| Glassine | A translucent paper enclosure that sticks to gelatin at high humidity and is considered unsuitable by ISO |
| ISO | International Organization for Standardization |
| Kappa number | A number indicating the relative amount of lignin in paper |
| Lightfast | A colorant resistant to fading from light |
| Lignin | A plant substance that binds cellulose fibers together and contributes to the deterioration of paper and photographs |
| Migration | Movement of chemicals such as acid between adjacent materials |
| Out-gassing | Release of volatile contaminants, the main route by which harmful substances reach photographs |
| Oxidation | Loss of electrons, the cause of silver fading in black-and-white photographs |
| pH | Scale of acidity and alkalinity; 7 is neutral, lower is acidic and higher is alkaline |
| pH testing pen | A pen containing indicator dye for assessing surface pH |
| Pigment | An insoluble colorant, more stable than dye but with a narrower color gamut |
| Plasticizer | An additive that makes plastic flexible; flexible PVC releases it onto the image |
| Polyester | A plastic considered safe by ISO for photo enclosures, provided it passes the PAT |
| Polypropylene | A plastic considered safe by ISO for photographs, provided it passes the PAT |
| PVC | A plastic considered unsafe by ISO because of plasticizers and possible release of hydrochloric acid |
| Rag paper/board | Paper or board made of long cotton fibers and free of lignin |
| RH | Relative humidity of the air; ISO recommends a range of 30% to 50% |
| Silver image interaction | Any reaction that alters the metallic or ionic silver of a black-and-white photograph |
| UV light | Electromagnetic radiation from 300 to 400 nanometers that contributes to the deterioration of photographs and paper |
| Water-soluble | A substance that dissolves in water |
Source:Eastman Park Micrographics(epminc.com)(opens in a new tab)
Frequently asked questions
Which materials are not suitable for contact with photographs?
Acidic materials, lignin, flexible PVC and glassine are not suitable for contact with photographs.
What relative humidity does ISO recommend for storage?
ISO recommends 30% to 50% relative humidity for storage.
Which plastics are considered safe for photo enclosures?
Polyester and polypropylene are considered safe by ISO for photo enclosures, provided they pass the PAT.
How does UV light affect photographs?
Reducing UV exposure extends image life.
What is out-gassing?
Out-gassing is the release of volatile contaminants, the main route by which harmful substances reach photographs.
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