Acid Migration

Acid Migration

Overview

Acid migration is the process by which acids present in one material leach into an adjacent material, such as artwork or mat board. This transfer gradually weakens and discolors the affected material, significantly reducing its longevity. In picture framing, acid migration is one of the most common causes of long-term damage to paper-based artwork, photographs, and textiles.

How Acid Migration Occurs

• Contact with acidic materials: When acidic boards, mats, or papers are in direct contact with artwork, acids naturally move into the neutral or alkaline fibers.
• Environmental factors: High humidity and heat can accelerate the migration of acids between materials.
• Storage conditions: Prolonged storage in poor-quality containers (e.g., cardboard boxes with lignin content) increases the likelihood of acid transfer.

Effects on Artwork

• Discoloration: Visible yellowing or brownish stains often referred to as "acid burn."
• Structural weakening: Paper becomes brittle, making it prone to tearing or cracking.
• Decreased value: Once acid migration has caused staining, it is often irreversible, lowering both the aesthetic and financial value of the piece.

Prevention and Solutions

• Use of barrier layers: Applying barrier tape or inserting acid-free interleaving sheets prevents direct contact between acidic and non-acidic surfaces.
• Buffering agents: Some conservation materials include buffering substances, like calcium carbonate, which neutralize migrating acids.
• Proper framing materials: Acid free or archival boards, mats, and adhesives significantly reduce risks.
• Conservation treatments: In some cases, professional conservators can wash or deacidify affected papers, though prevention is always preferable.

Framing Industry Context

Before the widespread adoption of acid free materials, acid migration was virtually unavoidable in picture framing. Common cardboard and wood-pulp mats, popular in the early 20th century, often transferred acids into valuable works. Today, conservation framers rely on archival standards and protective barriers to ensure that acid migration does not compromise the artwork. Preventative measures are now a standard expectation in professional framing.

Related Terms

• Leeching
• Barrier Tape
• Buffering
• Acid Outgassing