Acid-free, buffered, inert: reading the labels on archive supplies

What to take away

Where the acid comes from

Paper made by hand from cotton or linen rag is long-fibered and strong. Paper made from wood fiber since the nineteenth century usually is not. The Canadian Conservation Institute's guidance on caring for paper objects explains why: wood pulp gives shorter fibers and may contain lignin, which discolors the sheet, and acidic methods such as groundwood pulp produce poor-quality paper.

It notes the modern exception too: paper comparable to rag in longevity can be made from highly processed chemical wood pulp with an alkaline material such as calcium carbonate added.

The same guidance names two chemical pathways. Acid-catalysed hydrolysis is greatly accelerated by higher acidity in the paper or higher relative humidity. Oxidation is accelerated by metal contaminants, pollutants, bleach residue and light. Both end in loss of strength and change in appearance.

The timescale is the part worth remembering. At ordinary comfort temperature, around 20C, and moderate humidity around 50 percent, acidic or heavily contaminated paper can suffer significant damage in a few decades or less. That is why an old scrapbook browns the photographs in it, and why the cardboard carton is doing damage while it sits still.

What the terms actually claim

That last row is the one worth memorizing. Purified wood pulp can still form acids over time from residual processing chemicals, bleaching agents and air pollutants. That is why buffering exists: the alkaline reserve absorbs acid that appears later.

When buffered is wrong

Buffering helps paper. It does not help everything. Cyanotypes and diazotypes are sensitive to higher pH and want unbuffered enclosures, and the same caution applies to some photographic materials and to anything made from protein, including leather, wool and silk.

The practical rule is short. Buffered for letters, documents, clippings and most prints. Unbuffered for blueprints, for photographs you cannot identify, and for anything with fabric or hide in it. In doubt, unbuffered is the more conservative choice.

Choosing beyond paper

The Canadian Conservation Institute's technical bulletin on products used in preventive conservation reviews the storage products themselves, and it is unsentimental about plastics. Many plastic sheets and panels are expected to embrittle enough to tear or crack under stress within thirty to fifty years, and some polyethylene sheeting becomes brittle after only five.

It also notes traffic in the other direction: compounds migrate from dirty, acidic or oily objects into the products holding them, staining mounts and containers, which then stain the next object they touch.

Its rule on adhesives is the one to write down. Applying adhesive or tape directly to an object is unsafe and not recommended: it goes brittle or viscous, fails, and stains in ways that are hard to remove.

Adhesives belong in the construction of mounts, boxes and sleeves, never on the item. Every tape fails eventually, and the only question is when.

A short buying rule

Fit first, chemistry second, price third. An enclosure that is too large lets contents slump and crease, and no amount of alkaline reserve fixes a bent corner. Our first kit list sets the buying order, and the starting point guide covers the count that tells you what sizes to order.

Common questions