1 INTRODUCTION

The restoration and conservation of stone monuments and objects often involve impregnation with stone consolidating materials. However, to assess the effectiveness of such treatments, the migration and distribution of the materials inside the stone must be determined. The methods of measurement that have been investigated in the past have not been widely used in technical investigations and conservation practice due mainly to the need for sophisticated instrumentation or to their ineffectiveness in the case of some consolidants.

Iodine vapor is often used in the field of thin-layer chromatography for identifying organic compounds. It is physically adsorbed on the surface of many organic compounds and produces a yellow or light brown color. The colored complex that is formed is generally reversible, leaving the substance unchanged chemically after dissociation of the adsorption complex and evaporation of the iodine. Owing to this characteristic of iodine vapor, it was thought that it might be possible to visualize the location of consolidants in stone if similar physical adsorption of the iodine vapor occurs on the polymers that are frequently used for the preservation of stone. Since iodine vapor is not adsorbed and does not react with limestone, the consolidated areas should show up as a yellow or light brown color, leaving the unconsolidated area with no change in color.

The technique described here can be easily and rapidly carried out, and it appears to solve many of the problems associated with visualizing the location of consolidants in limestone and probably other types of porous stone as well.