An acid-free mat is a type of mat board manufactured within a pH-neutral range to ensure the long-term preservation of artwork, photographs, or documents. By eliminating harmful acids, these mats protect against staining, discoloration, and deterioration. Acid-free mats may be naturally pH neutral or chemically treated to achieve archival safety.

Manufacturing Process

Natural neutrality: Some mats are made from pure materials such as cotton linters, which are naturally acid-free.
Buffered treatment: Others are created from wood pulp or mixed fibers and undergo a buffering process that neutralizes acids and stabilizes the mat at a pH-neutral or slightly alkaline state.
Chemical reinforcement: Alkaline buffers may be added to prolong resistance to acid migration over time.

Uses in Framing

Artwork protection: Prevents direct acid contact between artwork and surrounding materials.
Aesthetic enhancement: Frames the piece with a decorative border while maintaining conservation quality.
Layering: Used with museum board or backing boards for added archival safety.

Advantages

Archival safety: Protects against yellowing, acid burn, and brittleness caused by acidic mats.
Wide variety: Available in different colors, textures, and thicknesses such as 4 ply and 8 ply.
Cost-effective: More affordable than the highest-grade rag mats but still provides solid protection.

Comparison to Other Mats

While acid-free mats provide significant protection, they differ from museum board, which is made entirely from cotton fibers and considered the gold standard for preservation. Similarly, rag mats utilize cotton content for superior longevity. Buffered mats, on the other hand, add alkaline reserves for extra protection, making them useful in environments where acidic migration is likely.

Framing Industry Context

The widespread availability of acid-free mats marked a turning point in modern framing practices. Previously, mats made of acidic paper often caused irreversible damage to artwork. Today, acid-free mats are considered the baseline for conservation framing, ensuring that framed works are not only aesthetically pleasing but also safe from chemical harm over time.

Acid-Free Mat