Methylmagnesium cabonate, prepared by carbonation of a solution of magnesium methoxide, is compared with the magnesium methoxide as a deacidification agent for paper. Although the two materials are equally effective in deacidification and in prolonging the life of the paper, the methyl-magnesium carbonate is two to 10 times as stable to water, depending upon the solvent used. This stability avoids premature precipitation, minimizes surface deposits, and increases the interval between cleanings of equipment, making the solution much more convenient to use. The use is covered by U.S. Patent No. 3,939,091, February 17, 1976, assigned to the Library of Congress. A royalty-free, nonexclusive license will be available. See also AATA 15-389.