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Technical Column

Update October 5, 2009

By Virgil Elliott

ARC Living Master™ Virgil Elliott has provided the following update to his Technical Column 2001 on ARC.

Since I wrote my previous technical column, several important discoveries have been made that serious oil painters should know about. The latest word from Marion Mecklenburg, Senior Research Scientist at the Smithsonian Center for Materials Research and Education of the Smithsonian Institution, the scientist who was testing various things when I last wrote here, is that zinc oxide, aka zinc white, appears to be principally responsible for enough defects in oil paintings that it should be regarded as a problematic pigment. It has been identified as the key factor in delaminations between oil paints and acrylic grounds on stretched canvas. This includes white paints in which zinc oxide is a minor component in mixtures with titanium dioxide (titanium white) or basic lead carbonate (many brands of flake white). Dr. Mecklenburg stresses the point that the delaminations take place not only at the interface between the ground and the paint film, but occur between layers of oil paint as well, and that the problem is not limited to oil paintings on acrylic grounds. The extreme brittleness and the rapid rate at which zinc oxide oil paint becomes brittle seems to be the main factor in the problems, where the support is stretched canvas.

Whether this completely exonerates acrylic grounds (commonly known as acrylic gesso) from suspicion regarding their suitability for use as a ground for oil painting is yet an open question. One very knowledgeable art materials technical consultant with thirty-something years of experience in the field, George Stegmeir, estimates that under optimal conditions, the adhesion between acrylic grounds and oil paint layers is perhaps 80 percent of the adhesion between an oil ground (white lead in linseed oil) and oil paint, which he feels is adequate. The reason the percentage is not 100% is that there is no chemical bonding created between acrylic grounds and oil paint, but only a mechanical bond, whereas with an oil ground, a chemical bond as well as a mechanical bond is established with oil paints. More testing by some of my ASTM colleagues is ongoing on that score, but among the things indicated thus far is that the issue is complicated by the fact that there is a wide range of acrylic grounds/primers on the market today that are not consistent from one to the next in their formulations or performance. Some require more coats than others to mitigate problems of oil strike-through, among the inconsistencies reported. And for oil painters who buy their canvas pre-primed, as things stand now there is no way of knowing which product has been used to prime a given canvas, or how well it can be expected to perform over the short or long term. The ASTM Subcommittee on Artists' Paints and Materials is currently in the process of writing standards for acrylic grounds and for pre- primed canvas for artists' use. Artists are encouraged to attend and participate in the meetings.

The 80 percent adhesion figure may well be adequate for rigid panels and for canvas glued to panels, but for stretched canvas there might (or might not) still be more cause for concern. Stretched canvas is subject to deterioration in a much shorter period of time than a rigid panel, and much more susceptible to damage. It becomes weaker and less stable with time, while oil paint films lose their flexibility as they age, and ultimately become brittle. It's reasonable to expect problems to occur with a brittle paint layer on a flexible support with a flexible ground to which the oil paint had only a mechanical bond in the first place, 80 percent as well adhered as it would be with a good oil ground. And as for what constitutes a good oil ground, that issue, too, is somewhat complicated in our time. Lead carbonate in a linseed oil binder has been the traditional oil ground for centuries, and it has stood the test of time. But concerns over the toxicity of lead have driven many manufacturers to discontinue its use for oil painting grounds. Their new formulations are based on titanium dioxide and/or zinc oxide pigments, which lack the unique properties of lead that give it its durability. At least one highly regarded European company advertises its use of zinc white as the basis for the ground on its oil-primed canvas, despite what is now known about the problems with zinc oxide in oil paints. Titanium white in an alkyd binder may prove to be suitably durable, according to Marion Mecklenburg, whose tests are now far enough along to give good indications of potential long-term performance. The same might not be said of titanium white bound in oil rather than alkyd, as alkyds bring an extra measure of durability to the ensemble.

The conscientious, cautious oil painter whose work sells for respectable prices might well eschew the convenience of acrylic grounds for stretched canvas, or pre-primed canvases labeled as primed for "universal" media until more information is known about them as regards their suitability for oil painting, and stick to oil-primed canvas with white lead in linseed oil or titanium dioxide (without zinc oxide) with an alkyd binder. Gluing canvas to rigid panels would mitigate many of the potential problems, of course, by immobilizing the paint film.

Sizing, the material used to prevent oil absorption by the canvas or panel, must also be given consideration. I will address that in the next installment of this column. Astute art collectors are beginning to realize the importance of proper materials and combinations of materials in the paintings they consider buying, as well they should. High prices depend on the connotation of quality, and the concept of quality includes the materials of which something is made. It is entirely reasonable to expect what one has paid dearly for to hold up for more than a single generation. It reflects badly on artists in general when faulty materials or craftsmanship cause their creations to develop problems after they've been sold for substantial prices. There is a real need for artists to once again embrace high standards of workmanship and professional pride, if we can realistically expect to ever be taken seriously again. Too many decades of too little concern for such matters have led to too many regrettable instances of artworks falling apart prematurely, and this has contributed to the perception of the artist as flaky oddball clown or lunatic. Surely no artist benefits from that stereotype.

Click here to see Virgil's original column.

Virgil Elliott is the author of Traditional Oil Painting: Advanced Techniques and Concepts from the Renaissance to the Present, published in 2007 by Watson-Guptill Publications. He is one of ARC's Living Masters, and an active member of the ASTM Subcommittee on Artists' Paints and Materials. Images of some of his artworks can be seen in ARC's Gallery of Living Masters and on his own web site, www.virgilelliott.com.


Technical Column Update 2009
Technical Column 2001

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