3 3. PENETRATION INTO SANDSTONE

In order to evaluate the penetration of cyclododecane into stone substrates, sandstone samples were treated via various delivery methods. Only sandstone was considered in the initial testing phase for use of cyclododecane on stone substrates; further evaluation of consolidant sublimation included limestone samples as well. Cyclododecane was applied to six cores of Ohio Massillian sandstone, measuring approximately 3 cm in length and 0.5 cm in diameter. Saturated solutions of cyclododecane in hexanes and Shellsol OMS were applied with a brush directly onto one end of the samples; two samples were treated with each solution. The initial depth of penetration, as evidenced by the solvent-saturated surface, was marked with a pencil line immediately following treatment. During the 5–15 minutes following treatment, any further movement of the solution was noted with a second pencil line. Because the 0.5 cm diameter of the core samples provided only a small surface area, melted cyclododecane was painted along one length of two samples. Samples were left overnight to permit solvent evaporation. The untreated ends and lengths of the stone samples were then partially immersed in aqueous dye solutions. The dyes were absorbed by capillary action into the untreated portions of the stone samples, but were repelled by the hydrophobic consolidant, resulting in a visible division between treated and untreated areas.

On those sandstone samples treated with melted cyclododecane, the absorbed dye fully saturated the stone and was visible beneath the melted cyclododecane coating, thus illustrating that little or no consolidant penetration had occurred. These stone samples were not warmed prior to treatment, and the consolidant solidified upon contact with the stone surface. Other research has noted varying depths of penetration for melted cyclododecane applied to porous substrates that have been warmed prior to and during consolidant application (Hangleiter 1998b; Riedl and Hilbert 1998; Br�ckle et al. 1999). Penetration of melted cyclododecane up to 1 cm was observed via cryo-SEM by Riedl and Hilbert (1998), while the volatile solvent petroleum ether was observed to carry the consolidant only 2–3 mm into the substrate. On those sandstone samples treated with solvent solutions, the aqueous dye traveled into the unconsolidated stone beyond any notations of secondary penetration and up to the pencil line that marked the initial penetration, at which level the aqueous dye solution was repelled by the hydrophobic consolidant. This absorption of the aqueous dyes suggests a chromatographic effect in which the solvent solutions carried the cyclododecane only as far as initial uptake achieved during application. Any additional penetration beyond the initial uptake therefore appears to reflect the movement of solvent only. Depth of penetration appears variable by solvent evaporation rate, with the slower-evaporating Shellsol OMS solution delivering cyclododecane farther into the sample. Such observations relating to the uptake and penetration of consolidant systems are preliminary, and further testing is needed to more fully evaluate the depths of penetration that can be expected for various consolidant systems applied to different substrates.