Irregular Paint Gloss: Solving Uneven Sheen in Artworks

An irregular paint gloss on an oil painting can often result in a patchy appearance even after the varnish is applied. In this article, we discuss how to fix this on an existing painting and how to avoid it in the future.

An irregular sheen on an oil painting is often linked to paint with high pigment volume concentration (PVC). The paint contains air voids due to a lack of binder. Freshly applied paint “sinks” into the underlying substrate. “Sinking in” is a common phenomenon among oil painters. This is the most frequent issue we encounter teaching artists in our Painting Best Practices courses. Let’s review the causes of sinking in:

Excessive Use of Solvents

This is one of the problems of using solvents in oil painting. Solvents reduce the viscosity of oil, making it easier for the underlying substrate to absorb it. When oil sinks into the layer below, it increases the pigment volume concentration (PVC). This creates air voids in the paint film as it dries, resulting in a rougher surface texture. The rough texture, in turn, scatters more light, causing a dull matte appearance, which should otherwise be satin to glossy. Reducing or avoiding solvents altogether helps to eliminate sinking in and patchy sheen.

Excessively Absorbent Grounds or Supports

One way to avoid non-uniform gloss is to paint on less absorbent grounds. Most artists never consider how the ground affects the overall painting. This is the same as failing to properly consider the foundation of a house. The ground is as important, and perhaps more important, in some aspects than the upper paint layers.

Excessively absorbent grounds can cause oil paint to sink in. Many artists paint on grounds that are too absorbent. Acrylic grounds are very absorbent, yet they are one of the most widely used grounds for oil paintings. Oil grounds are typically less absorbent than acrylic grounds. The grounds of pre-primed canvases—even those with oil grounds—are often very absorbent. Painting on oil grounds reduces the phenomenon of sinking in. Applying additional coats of oil ground to an existing ground reduces its absorbency and the potential for sinking in.

Sinking Colors

Certain pigments are more prone to sinking in than others. Umbers usually come to mind when painters think of colors that sink in. These pigments contain a larger volume of oil and, therefore, have a lower critical pigment volume concentration (cPVC). The oil is readily absorbed by the underlying layer, giving dried paint films a matte and usually non-uniform appearance.