Before beginning a rehousing project, it is important to determine what envelopes should be chosen for each item requiring rehousing.
When should polyester film encapsulation be used? Encapsulating is great for rehousing photographs and documents with many tears along the edges as it prevents direct handling of the record, it reduces the opportunity for further tearing. It is also water resistant, strong, flexible, smooth (it will not cause abrasions), and it is chemically and physically stable. There are, however, a few disadvantages to using polyester film encapsulation: it has static cling, it is relatively expensive, and it acts as a closed chamber containing off-gases.
Do not encapsulate:
- Blueprints, they off-gas ammonia
- Cellulose Nitrate Negatives, they off-gas nitrous oxide and nitrogen dioxide
- Cellulose Acetate Negatives, they off-gas acetic acid
- Fine Art on Paper with Friable Media (pastels, charcoal, etc.), the static cling can remove loose media
If using paper envelopes or folders, when should unbuffered or buffered be used? Never used buffered envelopes or folders to rehouse blueprints or cyanotypes because the blue colour (Prussian blue) will begin to turn pink; the colour is dependent on the pH level.
Always contact a conservator prior to rehousing fine art on paper as certain colours may be affected by buffered material.
Use Buffered Material for:
- Cellulose nitrate negatives
- Cellulose acetate negatives
- Yellowed documents
- Documents with iron gall ink
- Documents with adhesive or glue residue
- Maps without blue media
Use Unbuffered Material for:
- Vellum or parchment
- Coloured photographs
- Black and white photographs
- Polyester negatives
- Maps with blue media