A procedure for non-destructive pH determinations of cellulose matrials which comprise the paper in books and documents in libraries and government archives is described. Because the useful life of most paper now in existence is primarily a function of the acidity of the paper, it is necessary that the pH be known so that appropriate preservation and/or restoration techniques may be employed to extend the useful life of books and documents which cannot be destroyed or otherwise defaced for the purpose of pH determination. This method is accurate and does not require destruction or extensive soaking of the paper samples to be tested.