We have been asked many times over the years to provide oil content information for Williamsburg colors, Extender Medium and Oil Grounds. To answer that request, we have created a chart organizing these products into four categories – Low, Moderate, Medium, and High oil content by volume. We have chosen oil content by volume, because percentage of oil by weight can be misleading, especially with heavier pigments such as cadmiums, iron oxides and lead white. We have also included dry time, as that is a prime consideration when layering colors. The chart is divided into two sections. In the top section, the colors are in order from lowest to highest percent oil content by volume, with the accompanying dry time for that color. The bottom section is organized from fastest to slowest dry time with the oil content for each color.
While oil content by volume may guide some painters in their practice, there are a myriad of other potential factors that go into making a painting. Unfortunately, providing a specific set of rules, that if followed, will give a consistent and positive result, is not realistic. At the very least, integrating this new oil by volume information as part of a commonsense approach to fat over lean, thick over thin and slow drying colors over faster drying colors, can provide a foundational approach to layering oil paints.
Fat Over Lean in Oil Painting
Oil by volume information may be helpful when making decisions about layering “fat over lean”. Within the fat over lean framework, the artist seeks to apply colors with more oil (fat) over colors with less oil (lean). In general, with all other factors being equal, applying leaner colors over those with more oil, could result in cracking.
For years we have advised that oil paints directly out of the tube are more or less considered lean, as they contain just above the minimum amount of oil to make a functional paste, called the critical pigment volume concentration. While the oil content in the tubed paint can factor into one’s approach toward fat over lean, we still consider the amount of oil binder, or oil medium, that is added to the tube paint as a primary consideration when following fat over lean protocols. In this case, the more oil binder that is added to the tube color, the “fatter” that layer becomes. Subsequently, due to the potential of oils and mediums to yellow, wrinkle and dry more slowly, applications with oil added to the paint should be applied more thinly and in the upper layers of the work.
Oil by volume and fat over lean are only one aspect of a complex series of potentials that can impact the aging and long-term stability of an artwork. Oil paintings are dynamic systems that continue to change for decades and even centuries! An oil painting can be impacted by the types of pigments or oils it contains, as well as environmental factors such as relative humidity and amount of UV light it is exposed to. The preparation, quality of materials and technique used to make the oil painting also matter: the substrate type and quality, absorbency of the ground, type and amount of driers and other ingredients in the paints and mediums, and the uniqueness of the paint applications all play a role in how the work will age. And we cannot leave out the care required to protect and maintain the work either!
After 600 years, we are still learning how oil paintings age and transform over time. Each artist has to manipulate the materials at their disposal to make the most compelling work they can. If successful, the works will be cherished and cared for by future generations and hopefully provide further insights about combining materials in unique ways. For now, we hope the Williamsburg Oil Content by Volume Chart (linked above) will help guide your decisions and provide the information you need to make great paintings.
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