The Alkaline Advantage
Many manuscripts from the Islamic Golden Age, written on Samarkand paper, survive in excellent condition after more than a millennium. Modern paper made after the mid-19th century often yellows and becomes brittle in just 50 years. The chemical difference is a matter of pH. Most modern paper was produced using an alum-rosin sizing, which creates acidic conditions. In the presence of moisture, acid breaks down the long cellulose chains that give paper its strength, a process called acid hydrolysis. This reaction is self-catalyzing; as the cellulose degrades, it produces more acids, accelerating its own destruction.
Samarkand paper, however, is alkaline. While the exact historical recipes varied, the process resulted in a paper with a natural alkaline buffer, likely due to the local water and processing techniques. This alkaline reserve, which functions similarly to the calcium carbonate (CaCO₃) added to modern archival paper, neutralizes acids. It counteracts both acids absorbed from atmospheric pollutants like sulfur dioxide and those generated naturally by the aging of cellulose itself. By preventing acid hydrolysis, the paper's long cellulose fibers remain intact, preserving the paper's strength and flexibility for centuries.