Varnish Time

One of the most satisfying moments of a painting is applying varnishing.

The varnish application process

• Step 0 — Wait 6 months for the oil painting to dry. Less than this and you run the risk that the paint surface hasn’t sufficiently cured (a process called polymerization) to isolate the pigment layer from the varnish layer. Varnishing over a still-curing paint surface means the varnish can become difficult or impossible to safely remove and reapply later on.
• Step 1 — Thoroughly dust the surface. Using a clean, dry brush, go over the entire painting surface. Over the six months of waiting for this moment, a fair amount of dust and other particulates will have attracted themselves to the canvas. If you don’t remove them now, they will permanently become part of the varnish layer.
• Step 2 — Apply a thin, even coat. Apply a single, thin coat across the entire surface of the painting. For this particular portrait, I used a custom mix of 1-part Gloss to 2-parts Satin varnish. The Gloss allows the relatively darker background to continue to sing, while the Satin keeps the surface from becoming so mirror-like that ambient light creates distracting specular highlights.

• Step 3 — Give it a couple of days to dry. Once dry, the surface should be beautifully protected for the next 50 years or so.

The portrait of Theo was ready for varnishing so I did this one at the same time. The only real difference is that the ratio of Gloss to Satin in the mix was closer to 1:1. With a lighter background, I was less worried about loosing the dark passages here.

If you’re interested in the technical details of why varnish makes such a dramatic difference to the optical surface of a painting, check out the breakdown below.

Technical Details: What is “Sinking In”?

This optical magic really boils down to physical changes on the paint surface as the oil polymerizes and cures.

If you are familiar with frosted glass, you know that the “frosted” effect is achieved by creating a microscopically rough, uneven surface on one side of the glass. Because of this roughness, light rays hitting the surface don’t pass cleanly through the glass the way they do with transparent windows. Instead, the light bounces off the uneven surface in a scattered, diffuse pattern. This diffusion is what gives the glass its frosted, white appearance (it is also exactly why clouds appear white to us).

Oil paint, at its most basic level, is just a finely ground pigment (often colorful dirt or metal particulates) floating in a binder like linseed or walnut oil. That’s really all paint is. However, because we use so many different types of pigments, there is a wide range of physical properties that make each paint handle and behave slightly—or dramatically—differently.

You can imagine that some pigments show their colors most vibrantly when their particles are left relatively large and rough, whereas others will only sing if they are ground extremely fine and uniform. This means each pigment has a unique relationship to its binder, even if all your paints use the identical linseed oil vehicle.

Furthermore, oil paint shouldn’t be applied directly to a raw support. For best results, it is best practice to apply a “ground” layer of acrylic gesso. For my work, I generally paint on aluminum panels (specifically ACM panels) which I slightly abrade before applying four layers of gesso to prepare the surface.

This ground layer is semi-absorbent by design; you want the oil paint to form a solid, permanent adhesion to keep it from flaking off decades later. It’s a necessary feature.

However, remember that different paint pigments have highly variable physical characteristics. A pigment particle that is larger and rougher in shape interacts with the oil vehicle very differently than one that is ultra-fine and regular.

When you combine these different pigment demands, the absorbency of the underlying gesso ground, individual handling variations, and the fact that oil paintings are built up in multiple reworked layers, you get an uneven surface layer. You will get areas where the oil fully saturates the ground or clings to the pigment to create glossy patches. In contrast, you will get other areas where “thirsty” pigments or the ground layer below absorb more of the oil, leaving the pigment particles starved and exposed near the surface.

This is exactly what happens in areas where the dry paint looks flat or matte (a phenomenon artists refer to as “sinking in”). Just like the frosted glass, these starved pigment particles create a microscopically rough, irregular surface. Light hitting these patches scatters in a diffuse pattern, causing the pigment to lose its natural luster and appear dull to our eyes.

Beyond the physical protection it provides, the final varnish layer introduces a perfectly uniform liquid plane that floods and fills in all of those microscopic valleys. By eliminating the rough surface texture, it allows light to transmit evenly and consistently to the pigment beneath. As a result, the scattering effect vanishes, instantly restoring the clean, saturated colors and deep values exactly as they looked when the paint was wet.