This report describes the results obtained during the carrying out of the first phase of a study to evaluate commercial mass-deacidification processes. Phase I involves the examination of four naturally-aged papers of various dates (1728 to 1948) and fibre content (wood pulp or linen; with or without lignin) which had been treated with AKZO, FMC or Wei T'o deacidification processes. Analyses were performed before treatment, after deacidification and after artificial ageing at 50per thousand RH and 80°C. The techniques used monitored degree of degradation of the paper (degree of polymerization, zero span tensile strength, and carbonyl content), distribution of buffer reserve (surface pH, atomic absorption) as well as other important characteristics such as penetration of buffer into the paper sheet (scanning electron microscopy/microprobe analysis), amount of buffer deposited into the sheet (alkaline reserve), and overall pH of the sheet (cold extraction pH).