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We have reacted Georgia marble in sulfur dioxide (S02) enriched atmospheres and calcul~ted the reaction rate constant. This constant was denved from surface reduction data, obtained by leaching the reaction product from samples exposed for different periods of time. Application of this constant to marble weathered in known ambient levels of sulfur dioxid~(SO2) and relative humidity, .allows the prediction of the thickness of the resulting gypsum crust formed over a given period of time. We have found that the crust grows outwards due to calcium ions which migrate from the interior and then react with sulfur dioxide at the sample surface. Thus, any treatment of the sulfated marble should include the considerations that the crust only masks the marble surface and is not an integral part of the original sculpture, and that cavities exist in~he u:nderlying layer of marble from which the calcIum Ions were selectively depleted.

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