THE USE OF IMMISCIBLE SOLVENT COMBINATIONS FOR THE CLEANING OF PAINTINGS
THERE HAS BEEN considerable debate of the use of various solvents and combinations of solvents for the cleaning of paintings. One common choice in selecting a cleaning solution is to combine an active solvent, such as ethanol, isopropyl alcohol or acetone, with a relatively inactive solvent, such as Stoddard solvent (white spirit), petroleum spirit or turpentine. This paper considers the role of moisture in such a system.
I had noted that some traditionally apprentice-trained conservators from Europe would add some water to the cleaning solution. A typical cleaning solution might be 30% ethanol, 65% turpentine and 5% water by volume. Such a solution separates into two immiscible layers (phases). These were shaken into a cloudy suspension each time a swab was taken.
Similarly, should a solvent mixture like 15% ethanol (or isopropanol) and 85% white spirit be chosen, it is likely that it will separate into two layers if there is sufficient water in the ethanol (as anhydrous ethanol will absorb moisture from the atmosphere). A water content in the order of 5% in the ethanol or 1% of the combined cleaning solution is sufficient for this separation to occur.