Industry
Part of How to sequence a family photograph project from triage to storage
Risk in a photo archive: it follows the material, not the subject
Risk in a photograph collection follows the material, not the subject. How to spot nitrate and acetate film, cased images and color, and what each one needs.
What to take away
- Sort by material before sentiment. The picture you care most about is often the most stable thing in the box.
- A vinegar smell in a negative box is not mustiness. It is film decomposing, and it speeds itself up.
- Cased images from the nineteenth century are metal and glass, and they never go in a freezer.
- No practitioners were interviewed for this article. It describes published material science, not opinions.
Why this is not a maker profile
The headline this page was generated under promised a look at how independent practitioners work. That would take interviews, and none were carried out. What can be given instead is the basis those practitioners actually use, which is what each photographic material is made of and how it fails.
Film negatives: the material that has a clock on it
The Canadian Conservation Institute's note on care of black-and-white photographic negatives on film divides film supports into three categories. Dates matter. Cellulose nitrate: from the 1880s, discontinued by its largest maker in 1951.
Film supports over time
- 1880sCellulose nitrate introduced
- 1920sCellulose acetate introduced
- 1950sPolyester introduced
- 1951Nitrate discontinued by largest maker
Measurements concern nitrate. The material is highly flammable, reported to ignite spontaneously, and inherently unstable. But spontaneous ignition has occurred only in large-volume storage, such as motion picture film exchanges.
Single negative sheets in individual envelopes, or several sheets interleaved in one envelope, do not constitute a spontaneous ignition hazard.
Acetate is the more common household problem. Some early safety films from the 1930s and 1940s suffer severe shrinkage as solvents and plasticisers are slowly lost, and the shrinking base wrinkles the gelatin layer until no good print can be made from the negative. Salvage means stripping the gelatin onto a new support, which is labor-intensive specialist work.
The warning sign is a smell. Acetic acid in a storage box means the acetate is decomposing, and that decomposition is autocatalytic, so a bad box gets worse faster on its own. Isolate it.
Cased images: old, tough, and easy to ruin
The Canadian Conservation Institute's note on the care of encased photographic images covers three types found in nineteenth century cases: the daguerreotype, introduced in 1839, and the ambrotype and tintype, both wet collodion process, from the 1850s.
Daguerreotypes continued into the 1860s, ambrotypes a little longer, and tintypes survived into the twentieth century as an instant portrait format.
It also gives the identification trick. A daguerreotype is a silver image on a silver-plated copper sheet. Photographically, it is a negative.
Turn it in the horizontal plane so light strikes at a different angle. In certain positions the picture appears as a negative. That mirror quality tells it from an ambrotype.
Leave these sealed in their cases and packages. The seal is doing work.
A risk order for a household box
| Material | Risk | First action |
|---|---|---|
| Acetate negatives with any vinegar smell | Highest | Isolate, then copy |
| Color slides and prints | High | Copy, then keep dark and cool |
| Nitrate negatives | High but manageable | Individual envelopes, cool, ventilated |
| Cased images | Low if undisturbed | Leave sealed, store flat |
| Fiber-base black and white prints | Lowest | Sleeve and file |
Our plan for a photograph collection covers conditions and sequence, and the piece on what actually drives the cost covers what copying a risk batch is worth.
