What Acid-Free Means in Practice
Paper and board are described as acid-free when their pH is 7.0 or above at the time of manufacture. A pH below 7 indicates acidity — hydrogen ions that attack cellulose chains and cause paper to yellow and become brittle over time. Ordinary cardboard, wood-pulp folders, and newspaper all fall well below neutral pH and release acids as they age.
Acid-free alone is not sufficient for long-term storage. The material also needs to be lignin-free. Lignin is a compound in wood pulp that breaks down into acidic by-products. Even a pH-neutral board containing lignin will become acidic within years. Look for materials described as both acid-free and lignin-free.
Alkaline Reserve
Archival-grade board and paper typically include an alkaline buffer — commonly calcium carbonate — at a concentration that neutralises acids migrating from adjacent documents or from the atmosphere. A 2–3% alkaline reserve, as specified in standards such as ISO 9706 (for permanent paper), gives the material a margin against incoming acid rather than just starting at neutral pH.
What to Look For on Product Labels
When purchasing storage materials, useful indicators include:
- ISO 9706 — the international standard for permanent paper; requires pH 7.5–10, at least 2% alkaline reserve, and low lignin content.
- PAT (Photographic Activity Test) — particularly relevant for materials stored with photographs or mixed-media items; tests for harmful off-gassing.
- pH 7.0–8.5 stated on packaging — a basic indicator for folders and boxes.
Terms like "archive quality" or "conservation grade" without supporting standards are not reliable indicators on their own.
Types of Materials Needed
Boxes and Folders
Clamshell boxes, drop-front boxes, or flat document boxes made from lignin-free board provide the outer environment for a collection. Folders inside the box separate individual documents and prevent them from resting directly on each other.
Interleaving Tissue
Unbuffered acid-free tissue (not buffered, for items with coloured media) or buffered acid-free tissue (for plain paper documents) is placed between sheets or prints. It prevents direct contact and absorbs minor moisture variations.
Polyester Sleeves
Clear polyester (Melinex or Mylar grade) sleeves allow documents to be viewed without direct handling. Avoid PVC sleeves — PVC off-gasses plasticisers that migrate into paper.
Sourcing in Poland
Archival materials are available from specialist suppliers. The National Archives of Poland (Naczelna Dyrekcja Archiwów Państwowych) publishes guidance on approved suppliers for state institutions; some of these suppliers also sell to private buyers. Conservation supply companies based in Germany and the Netherlands ship to Poland with reasonable lead times for individual orders.
Standard office supply shops in Poland do not generally stock lignin-free board. Items labelled "archiwalne" in Polish office contexts may refer to long-term filing rather than conservation-grade materials — check pH and lignin specifications before purchasing.
Adhesives and Fasteners
Metal staples, rubber bands, and ordinary adhesive tape should be removed from documents before archival storage. Metal fasteners rust and leave staining; rubber bands harden and fuse to paper; acidic tape residue is extremely difficult to remove once it has set. If fastening is necessary, use stainless steel staples with a barrier interleaf, or fold a strip of acid-free paper over stapled corners.