Varnishes and Surface Coatings: Solubility Test Description & Solvents Used in Solubility Tests

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Painting Conservation Catalog

Date: Submitted September, 1997
Compiler: Wendy Samet



Solubility Test Description

The solubility tables included in most specific varnish sections are the result of tests performed over a period of three months. Three grams of resin were placed in 10 ml of solvent in a 30 ml jar and allowed to stand. The jars were shaken occasionally. For the proprietary varnishes, a dilution test was devised using three grams of the commercial varnish diluted with 10 ml of the same solvents in the same type of jars. The words “Soluble,” “Partially Soluble,” and “Insoluble” did not adequately describe all of the various results of swelling, two-phase mixtures, and gels that resulted from dissolving materials with such a variety of molecular weights and polydispersities. Therefore, solubility terms and definitions were invented to better describe the results. These are practical tests designed to show which solvents a resin will dissolve in initially. With the exception of damar, these tests were done only once. If these tests are repeated, the results may be different due to differences in solvents, resins, or room conditions.

Please keep in mind that many of the low molecular weight resins have an initial solubility in hydrocarbon solvents that falls between the range of 0.1% to 99% aromatics. Some resins dissolve between 20–70% aromatics and these unique solubilities are not reflected in the solvent charts in this catalog. Solvent combinations were not tested. So, if a resin is soluble in Cyclo Sol® 100 (99.4% aromatic) and insoluble in petroleum benzine (~11.5% on this chart), it may be soluble in an aromatic blend in between.

The solvents xylene, toluene, acetone, isopropanol, ethanol, Arcosolv® PM, and petroleum benzine used for these tests are from the National Gallery of Art, Washington, D.C., and are frequently ordered and were available at the time of testing. The Shell Sol® 71, Shell Sol® 340 HT, Shell Mineral Spirits 145, Shell Cyclo Sol® 100, and Winsor & Newton, Turpentine English Distilled were purchased for these tests.

It is important to use new resins whenever possible to ensure the best aging of the varnish over time. In performing these tests, when aged resins were used, the solubility test results did not match those conducted with fresh resins. Keep this in mind when using these solubility tables. See the following page for the list of solvents used in the solubility tests.

Solvents Used in Solubility Tests

Odorless Mineral Spirits, Shell Chemical Company (aka Shell Sol® 71) aliphatic hydrocarbon, 0.1% aromatic

Stoddard Solvent/Shell Sol® 340 HT, Fisher Scientific. Presently Fisher Stoddard Solvent is Shell Sol® 340 HT, aliphatic hydrocarbon, 0.4% aromatic

Shell Mineral Spirits 145 EC, Shell Chemical Company, hydrocarbon, 7.1% aromatic

Petroleum benzine, Petroleum benzine, Fisher Scientific, Benzine petroleum naphtha B264- evaporation rate of n-Bu-Ac=2.0 (same as toluene) has a combined aromatic content of ~11.5%.

Cyclo Sol® 100, Shell Chemical Company (aka Cyclo Sol® 53) aromatic hydrocarbon, 99.4% aromatic

Xylenes, aromatic hydrocarbon, 100% aromatic

Toluene, aromatic hydrocarbon, 100% aromatic

Turpentine, English Distilled, Winsor & Newton, a distillate of crude pine resin consisting of a mixture of monoterpenes (sometimes with small amounts of sesquiterpenes)

Isopropanol, isopropyl alcohol

Ethanol, ethyl alcohol, reagent, denatured, HPLC grade, Sigma-Aldrich

Acetone, dimethylketone, HPLC grade

Arcosolv® PM, Aldrich Chemical (aka Propasol®, Glycol ether PM, 1-Methoxy-2-propanol or Propylene Glycol Monomethyl Ether)

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