Minnesota Mining and Manufacturing Company

James M Ripka

Robert P Arens

A porous material having a top surface and a bottom surface, and a dye applied to the bottom surface of the porous material. The dye is soluble in a volatile imaging liquid contained in a suitable marker, such that when the volatile liquid contacts the top surface of the porous media, the volatile liquid penetrates the porous media, dissolves at least some of the dye to provide a dye solution with at least some of the dye solution migrating to the top surface, and evaporates leaving a permanently visible mark of dye residue on the top surface of the porous material.

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Zimmerman, MN, United States of America

James M Ripka