Cellulose nitrate in family collections: recognize it before you store it

What to take away

Plastics are a category, not a material

The Canadian Conservation Institute's guidance on caring for plastics and rubbers organizes the subject around risk management rather than materials. That structure tells you what matters. It separates thermoplastics from thermosets, gives identification its own section, and singles out a group it calls malignant plastics. These are the ones whose degradation harms their surroundings as well as themselves.

It then works through the agents of deterioration in two groups. Those of general concern to plastics include dissociation, theft, pests, water and fire. Those of specific concern include physical forces, pollutants, light and ultraviolet, incorrect temperature and incorrect relative humidity. It treats the flammability of cellulose nitrate as a topic in its own right.

Its temperature section is the practically useful one for a household. It distinguishes cool storage at around 4C in a refrigerator from cold storage at around minus 18C in a chest freezer, and discusses when each is appropriate, alongside the separate effects of increased temperature, decreased temperature, and fluctuation. It sets its damp threshold at over 65 percent relative humidity.

The one to identify first

Cellulose nitrate is worth recognizing because it is both unstable and common in old family collections. The Canadian Conservation Institute's note on the display and storage of objects containing cellulose nitrate lists where it turns up.

The list is domestic: cutlery handles in imitation ivory, drafting set squares and drawing templates, toys and dolls, photographic film, eyeglass frames, protective and decorative lacquers, and household items from buttons to toilet seats. It was sold under trade names including Celluloid, Pyralin and Xylonite.

It also gives a dating rule that is genuinely usable. Undegraded, unfilled, unpigmented cellulose nitrate is colorless and transparent. For about fifty years until roughly 1920 it was the only light-colored transparent or translucent plastic commonly available. Objects with those characteristics acquired or made before that period are probably cellulose nitrate.

The reason to care is what degradation produces. It gives off acidic and oxidising nitrogen oxide gases. In closed drawers, cabinets and display cases with restricted ventilation these build to high concentrations. They corrode metals, embrittle and discolor organic materials, and accelerate further deterioration.

That reverses the usual instinct. A degrading nitrate object is one of the few things in a collection that should be less enclosed rather than more.

Record what you decided

Plastics are the part of a collection where the next person will have no idea what they are looking at. An object identified once and then unlabeled is an object that has to be identified again, probably by someone with less information than you have now.

Write it on the enclosure: what you think the material is, what led you to that, and the date. Note explicitly where you are unsure. A box labeled probably cellulose nitrate, clear, pre-1920, not tested is far more useful than a box labeled nothing, and it tells the next person which questions are still open.

Storing the rest

For everything else, the ordinary rules apply: cool, dry, dark, separately enclosed, and away from anything that is degrading. Where an item genuinely needs it, cool storage in a refrigerator is a recognized option rather than an improvisation.

Our guide to what documented projects actually show covers reading the evidence, and the notes on materials that quietly cause damage cover the wider plastics problem.

Common questions