Oil Painting Methods
I produce all of my oil paintings on linen canvas primed only with oil-based primer - I never paint on surfaces primed with acrylic. I've done many paintings on Artfix L64C, and have liked that well enough, although my favorite canvas at the moment is Claessens #13 double-primed. Currently, I most often use Williamsburg paint, although I've also used Old Holland in the past.
As for painting tools, most of the work gets done with the use of ordinary bristle brushes - I use rounds and filberts most often. In addition to bristle, I also use a selection of softer brushes to carefully smooth the paint surface, primarily because I don't like the distracting effects of glare that so often occur on the ridges of brush marks typically found in thicker applications of paint. I've lately been using brushes made by Silver, specifically their Bristlon (stiff bristle) and Silverwhite (soft, synthetic sable) series - I've found that these hold up quite well despite repeated use over time, and they don't fall apart during cleaning.
I'm a very tidy painter, and I thoroughly clean my palette every day. I like to return to a clean, organized palette and workspace.
Before beginning a painting, I typically tone my canvas completely with a wash of some neutral color, often a combination of ultramarine blue with some earth-tone like burnt sienna or transparent oxide-red. In this early stage of the work, the paint is thinned liberally with mineral spirits - I prefer the "Gamsol" variety made by Gamblin, since it lacks the sickening fumes that are common with most other solvents. I never use turpentine as a solvent, due to the harmful effects of its fumes - I always get terrible headaches from turpentine (in contrast, Gamblin's odorless mineral spirits seem to produce no ill effects for me).
Even while the undertone color is still wet, I'll often begin a fairly elaborate, monochrome under-painting before starting to work with color at all, since I like to know that the primary drawing issues have been resolved in the early stages of the work. This leaves me free to concern myself entirely with color as the painting develops, and it always makes the later stages of the work proceed faster and more confidently. I'll often begin working with a folded paper towel as a tool instead of a brush - I prefer the blue "shop towels," which are a bit more durable for the job and leave less lint debris in the paint. The early foundations of the painting can be established quite quickly in this manner, without even getting a brush dirty. Highlights can be rendered simply by wiping the paint away to reveal the white canvas below. At this stage, all of the paint remains very thin and transparent, and I'm careful to eliminate the occurrence of raised paint markings wherever I find them - while the paint is still wet, I meticulously flatten the work's surface in preparation for future layers of paint.
To thin my paint when necessary, I may lightly dip my brush into odorless mineral spirits (typically, Gamblin's "Gamsol" product), or I may use a small amount of refined linseed oil, or sometimes a combination of the two. There is a balance to be achieved in the thinning of paint, since free-flowing paint is desirable, but too much thinning can be destructive to the integrity and binding power of the paint. The addition of too much oil to the painting's surface can also lead to a yellowing of the work over time, so I strive to avoid the excessive use of oil as a thinning medium. I never use any of the thick, resinous mediums that are widely available, since these tree-derived resins are known to contribute to cracking and yellowing of the paint film.
I've been trending toward a more limited palette of colors during the past couple of years, and now rarely use more than five colors (including white) in the production of any painting. Cadmium Yellow and Cadmium Red generally suffice for the warm side of my palette, while Ultramarine Blue and Cerulean Blue are usually the source of my cool colors. I occasionally use Manganese Blue when I require a more saturated, aquamarine blue. I'm also fond of a Williamsburg pigment called Quinacridone Red, which can be used to mix very fine, pure purples. I sometimes turn to several earth tones, as well, including Raw Sienna, Naples Yellow, and Mars Orange (a more saturated and transparent substitute for Burnt Sienna, I've found).
My choice of a white pigment differs from one circumstance to another, and is one of the most important palette selections to be made. One would think that every white pigment was pretty much the same, but it's not true. My preferred white for most uses is Lead White, also known as Flake White. Lead White is extremely transparent, which is sometimes useful, and sometimes difficult. But it's absolutely reliable for mixing exact colors matches for overpainting - in stark contrast to its rival, Titanium White. Although Titanium is the most popular white pigment in use today, because of its opacity and strong covering power, I've found that this pigment darkens in value at it dries - colors mixed with titanium will shift in value, either noticeably or not, depending on whatever percentage of titanium is found in the mix. I'm amazed by how many painters have not noticed the value drift of titanium white - I spent years trying to determine which pigment was introducing the mysterious problem, before realizing that the culprit was titanium. For this reason, I avoid this pigment as often as possible, especially when an exact color match is required for overpainting. I typically use titanium only for the mixing of colors of the very brightest value, such as highlights, and when a very opaque application is needed.
Virtually every square inch of my work receives at least two applications of paint, since I'm a perfectionist and in search of a very specific result. The first pass in any area rarely hits the mark quite accurately, and requires further attention after the first layer has dried.
There is a long-standing rule in painting, however, generally expressed as "fat over lean," which simply means that the initial, underlying layers in a painting should contain less oil than the final layers applied on top. The problem results from a disparity in the rate of expansion and contraction between the layers. "Fat" or oily layers are more likely to expand and contract during the drying process and in response to changes in atmospheric conditions - the more oil, the more lateral movement of the paint film. If the lower layers are more oily and mobile than those on top, they can pull the more brittle top layers to pieces, resulting in cracking. As a result, it's necessary to ensure that the greatest percentage of oil is to be found in the top surfaces of the picture, which can expand and contract freely without causing damage.
I don't like to work on dry paint surfaces, so I always apply a thin veneer of refined linseed oil to any area where I intend to add an additional coat of paint. I always wipe off as much of this oil as possible - only the thinnest film is required to make the surface sufficiently slick, and to restore the glossy, saturated appearance of the underlying paint (which often takes on a dull, matte surface upon drying).
However, in applying oil to dry paint surfaces, I've found that these underlying layers often develops a glassy surface resistant to new oil - the oil can be seen to bead up, rather than laying down to coat the surface evenly. This apparently occurs because the oil in the underlying layer has risen up to accumulate at the surface during the process of drying. The more oil in any given layer, the more likely it is to develop this glassy surface - and, as in the case of the "fat over lean" rule, this is yet another argument for avoiding excessive use of oil in the early stages of the work. Since oily, glassy surfaces seem to resist new applications of oil, this would logically seem to undermine the chances of a reliable bonding between old and new paint layers - and it definitely interferes with the ability to manipulate fresh paint on such a surface - so I find it necessary to treat the troublesome surfaces before painting over them.
I do this by mixing some linseed oil with "Bon Ami" powder, a common, gentle abrasive used for household cleaning, made from harmless calcium carbonate. A small amount of powder is all that's required to perform the task. The powder is mixed thoroughly into a puddle of oil until the abrasive is reduced to tiny, invisible particles. I then use a brush, loaded with the powder/oil mixture, to carefully scour the surface of the painting in the area to be retouched.
Although the oil mixture initially beads up, it will soon begin to cling to the surface quite evenly - a sign, I believe, that the powder is abrading the paint surface. If this is done gently, and without too much powder in the solution, the surface can be altered without any visible harm to the paint layer (for instance, grinding away too much paint or otherwise changing its appearance). I've found that trying to perform this same function with a solvent like mineral spirits will invariably cause visible damage to the underlying paint layer, which can be difficult to hide even with a great deal of overpainting, especially if one intends to apply transparent glazes. The Bon Ami powder is much more gentle, and has the added benefit of lacking noxious fumes. After the surface has been adequately prepared, I use a paper towel to rub away as much of the excess oil as possible. No residual trace of the powder can be detected, and the next application of paint will adhere to the preceding one without any trouble.