Final answer:
Museum-quality mats are the only naturally acid-free/lignin-free mats, made from 100% cotton rag or alpha-cellulose, designed to preserve artwork and documents without causing damage over time.
Step-by-step explanation:
Museum-quality mats, also known as conservation or archival mats, are the only type of naturally acid-free/lignin-free mats. They are made from 100% cotton rag or high-quality alpha-cellulose and are essential for preserving artwork, photographs, and documents over a long period. These mats prevent yellowing and deterioration often associated with standard mats, which can contain lignin and acids. The acid-free nature of museum-quality mats ensures that they will not damage the items they come in contact with, making them ideal for use in framing valuable and sentimental pieces.