THE USE OF IMMISCIBLE SOLVENT COMBINATIONS FOR THE CLEANING OF PAINTINGS
3 INTERPRETATION OF THE RESULTS
- Whilst changing the ethanol component in our original solutions from 20% to 15% to 10%, we see that the ethanol component in the mainly ethanol phases remains much the same, i.e. around 80%. The solvent power of the active component in each cleaning mixture is therefore very similar. The mainly ethanol phase of systems 1, 2 and 3 are plotted on the Teas Chart shown in figure 1 (as the mainly hydrocarbon phases).
Teas Chart showing location of ethanol and hydrocarbon phases of immiscible solvent combinations relative to regions of peak oil swelling and varnish solubility.Whilst the solvent power of systems 1 and 3 are very similar, system 1 will tend to be more active in varnish removal because it contains many more ethanol-rich droplets.The rate of solvent action (and varnish removal) can be varied by changing the proportions of hydrocarbons to ethanol, whilst maintaining the solvent power of both ethanol and hydrocarbon phases around the same level. Similar variations in the proportions of ethanol to hydrocarbons in a miscible combination would result in substantial changes in solvent power. In immiscible solvent combinations, the hydrocarbons can be regarded as a diluent.
- The limitation of using the immiscible solvent combinations described is that the varnish has to be soluble (or swollen) by the ethanol phases plotted on the Teas Chart. Experience has shown that the use of miscible solvent combinations is required for many varnishes.
- If we compare cleaning solutions 1 and 5, we can observe that by adding more water to the initial cleaning solution, the hydrocarbon phase remains relatively unchanged after separation; however, the active ethanol phase has substantially more water and less hydrocarbons. Too much water in the ethanol phase could be a disadvantage in treating water-sensitive paintings, so the water content of this phase is best minimized by adding water drop by drop until separation occurs.
- There was an interesting observation in the analysis of the ethanol phase in Table 3, in that the hydrocarbons in it were largely aromatic. The active component therefore consists largely of ethanol with toluene, xylene and water. Since aromatic hydrocarbons tend to be more active solvents than saturated hydrocarbons, this needs to be taken into account when formulating cleaning solutions and plotting solubility parameters.