The evaluation of permanence of paper is generally based on two criteria: the pH value and the presence of an alkaline reserve (calcium carbonate) often determined by an acid effervescence test (see also <i>AATA</i><b> 25-1613</b>). When a negative reaction was obtained on samples from supposedly permanent papers, further research was undertaken to verify the presence of calcium carbonate; the percentage of this component was measured by energy dispersive x-ray analysis. It was determined that the amount of calcium carbonate was sufficient but not uniformly distributed in the paper. A series of tests is necessary to determine the exact amount of calcium carbonate when this amount does not reach 3%. -- AATA