Alkaline paper is engineered to resist the yellowing, embrittlement, and loss of strength associated with acidic papermaking. During manufacture, pulp is processed to remove or neutralize acids, and an alkaline buffer-most commonly Calcium Carbonate-is incorporated to provide a long-term reserve against future acid exposure. In framing, alkaline (often called "buffered") papers and boards are used for mats, backing, and enclosures when the artwork safely tolerates an alkaline environment.

How It's Made

Neutral/alkaline sizing and fillers: The mill substitutes acid-sensitive alum-rosin systems with neutral or alkaline sizings and adds alkaline fillers (typically calcium carbonate) to maintain a reserve.
pH adjustment: The wet end of the papermaking process is controlled so the finished sheet cures at or above pH 7.
Fiber choices: Higher-grade alkaline papers may use purified pulps with lower lignin content to reduce future acid formation.

Why Buffering Matters

A buffering reserve slows acidification caused by environmental pollutants, acidic mounting materials, natural oxidation of impurities, and migration from adjacent objects. The reserve neutralizes incoming acids before they degrade the paper's cellulose chains, helping maintain flexibility, color, and tensile strength.

When to Use Alkaline vs. Neutral/Unbuffered

Use alkaline (buffered) papers/boards for: Most printed works on modern paper, drawings in graphite/ink, posters, and general-purpose mats and backings.
Use neutral or unbuffered papers for: Some photographic processes, cyanotypes, blueprint-type processes, and media or dyes known to be alkali-sensitive where a buffer could cause change or staining.
Mixed-media caution: If an object includes components of uncertain sensitivity (e.g., early color prints, protein-based sizes), err toward neutral/unbuffered layers in direct contact and place buffered materials further away in the package.

Applications in Picture Framing

Matting: Buffered mats help slow acid migration into artworks on paper and reduce the risk of overall yellowing.
Backings: Buffered backing boards create a more stable microenvironment inside the frame, absorbing acidity migrating from the wall side.
Interleaving & storage: Buffered sheets can be used between stacked works on paper to mitigate acid transfer during storage.

Compatibility Notes

Photographic materials: Many modern RC prints tolerate buffered boards, but some historic or alternative photo processes prefer unbuffered contact layers.
Protein-based media: Certain inks, dyes, and sizes (e.g., animal glue sizes) may be more stable in neutral (non-buffered) environments.
Composite objects: If the artwork includes adhesives or mounts of unknown composition, avoid placing strong buffers directly against them.

Identifying Alkaline Paper

Labeling: Look for terms such as "buffered," "alkaline reserve," or "pH neutral with reserve."
pH indicators: Spot tests (with appropriate, non-invasive methods) can suggest surface pH, but labelling from reputable manufacturers is the safest guide.
Spec sheets: Technical data sheets often note the buffering agent (commonly Calcium Carbonate) and target pH.

Material Composition & Fillers

Calcium carbonate buffer: The most common reserve alkaline filler; it neutralizes acids over time.
Clay fillers: Materials like Kaolin Clay may be included to adjust opacity, brightness, and surface characteristics.
Trace additives: Minerals such as Zinc compounds can appear in certain formulations for brightness or fungistatic properties, depending on manufacturer.

Aging Behavior

Alkaline paper typically retains strength and color longer than acidic papers. The buffer helps counteract acids introduced from the environment or adjacent materials. Long-term stability still depends on fiber quality (e.g., lignin content), storage conditions (temperature, pH context, humidity), and light exposure.

Framing Workflow Tips

Contact strategy: Place unbuffered materials in direct contact if the artwork is alkali-sensitive; use buffered boards as secondary layers.
Edge sealing: Use archival tapes/hinges compatible with the chosen pH strategy to prevent migration paths for external acids.
Environment: Maintain moderate relative humidity and avoid extreme temperature swings to preserve the paper's alkaline reserve and dimensional stability.

Common Misconceptions

"Alkaline equals archival in all cases." Buffered != universally safe. Sensitivity varies by medium and process.
"Any white paper is alkaline." Brightness doesn't guarantee buffering or neutral/alkaline pH; always check specifications.

Alkaline Paper