Acid-free is a term commonly used to define materials that do not have acidic components, making them resistant to decomposition and discoloration over time. There are many synonyms for acid-free, including pH-neutral, alkaline, non-acidic, and archival quality. pH-neutral materials have a balanced pH level of 7, which makes them safe for use in conservation projects and artwork preservation. Alkaline materials have a pH level above 7 and are used for long-term storage of documents and photographs. Non-acidic materials are those without any acidic content and are used for a wide range of purposes, from bookbinding to creating acid-free tissue paper. The term archival quality refers to materials that are designed for long-term preservation and have a high degree of resistance to environmental factors that might cause deterioration.