6 CONCENTRATION DEPENDENCE OF COLOR

To determine if the color intensity shown in the iodine vapor technique is proportional to concentration of consolidants, two different concentrations of each consolidant were applied to the surface of limestone samples by brushing on two bands that were separated by untreated stone. These samples were then kept in an iodine vapor chamber for 5–10 minutes along with a control sample. After 10 minutes, it was found that the color intensity of each band, qualitatively, was directly related to the consolidant concentration (fig. 3).

Fig. 3. Variation in color intensity due to concentration variation of consolidant applied on Indiana limestone: stone A, Rhoplex AC-33; B, Rhoplex AC-630; C, Acryloid B-72; D, polyvinyl acetate; E, Eponex 1510 + Jeffamine T403; F, Bayhydrol 121;G, untreated control. Concentration of all consolidant is 10% in upper band and 3% in lower band.

These variations in color can serve as a qualitative indicator for determining the unknown concentration distribution of the same consolidant in stone. It is necessary that the stone material for preparing such references be the same stone in which the concentration profile of a consolidant treatment is to be determined.