This page is a work-in-progress detailing the materials and techniques involved in the process of oil painting. My plan is to propose a straightforward methodology of sound practice in the studio. My goal is not to present the reader with an encyclopedic overview of every aspect of the craft, but rather to outline recipes and methods that I have adopted in my own work with the most success. Once completed, it will include instructions on how to build an easel and a stretcher; how to stretch, size and prime canvas and panel; how to prepare whites; how to prepare and use oils, solvents and varnishes. I also plan to describe the process of painting itself with notes on paints, brushes, sound practice and general advice.
For more in-depth study, I strongly recommend to any oil painter interested in materials and techniques to visit the fantastic website on New England artist-alchemist Tad Spurgeon. He has been experimenting with various historical recipes, mediums, varnishes and pigments for decades and his contribution to the painting community is invaluable. His research has helped me a great deal in understanding the technical aspects of the craft and much of the information you will find here is an extension of his own work.
Most painters will probably want to buy an easel rather than build their own. This makes sense in most cases. One should however be aware that – as is always the case in our profit-driven economy – most suppliers try to raise prices by selling you features that you don’t really need. All a good easel really needs to be is sturdy, stable and easy to operate. Everything else is mostly superfluous. A very simple tripod design like this one is fine for most indoor painting situations.
For very large paintings, one might consider simply hanging the stretched canvas on the wall. For small work on panel, a foldable table easel is perfect.
The use of fabric as a support for paintings was an innovation of the 15th century. It’s main advantages over panel where twofold. First, it allowed artist to produce much larger works than was possible on wood. Second, these works were light and could easily be rolled up and transported. On the other hand — whereas wood required relatively little preparation and could last centuries when well cared for — canvas is an inherently weaker and more sensitive material which means that artists had to develop special techniques and precautions to ensure their works would last. Namely, special sizing and priming.
Ironically, canvas’ flexibility — while being a plus for weight and portability — is, by definition, ill-suited for oil paint. As paint ages it becomes progressively harder and more brittle. Canvas, on the other hand, remains flexible and reacts to humidity changes in the environment by shrinking and expanding. This antagonism between mobility and immobility is the cause of cracking in old paintings. The same logic holds, by the way, when this situation arises between paint layers themselves. This originated the famous ‘fat on lean’ adage. From a conservation standpoint, it is therefore of capital important that the flexibility all the layers of a painting be taken into account from size to varnish.
There are two main options when it comes to canvas: cotton ( “oil on canvas” usually refers to cotton canvas) made from the cotton plant and linen made from the flax plant. Linen is traditional and is more durable than cotton, it is also much more expensive. If you can afford linen, that’s great. If not, just bear in mind that cotton will deteriorate faster. Proper preparation becomes paramount in this last case.
Buying canvas in bulk can represent a substantial financial investment. For this reason, many artist are compelled to pick the cheapest option available. This will usually be thin cotton canvas. This is fine for studies and sketches. For larger, more serious work, however, I strongly encourage you to use the thickest, strongest canvas you can afford. It will last longer, be more pleasant to work on and open the door to more possibilities in the way of so-called ‘subtractive’ painting and sgraffito.
A note on pre-gessoed canvas: Bottom-line: don’t buy it. Although it may seem like a good idea to buy pre-gessoed canvas, one should bear three caveats in mind regarding this “convenience”. First, the quality of the priming is usually questionable at best. Second, once stretched, the surface will have to be primed anew anyway as this will inevitably introduce minute cracks throughout. Third, the priming is usually very thin and even. Not an inspiring surface to work on.
Sizing – Rabbit Skin Glue
Rabbit skin glue (RSG) has been used to size canvas, panels and paper for centuries. Sizing seals the support to prevent it from absorbing the oil in the gesso or paint which would lead to rot or to keep watercolors and ink from bleeding into the paper. It is produced by boiling the skin of the animal to extract its collagen. Sold as a powder or as small granules, it must be dissolved in water to create a glue solution. It’s long history has proven its durability and stability over time. In addition to this, one of the main advantages of using RSG over modern PVA sizing is that RSG contracts as it dries which tightens the canvas strongly and uniformly over the stretcher.
Artists can add various ingredients to the glue to give it different properties: a bit of honey or glycerin makes the film more flexible; formaldehyde inhibits the growth of mold; alum counteracts the hygroscopic (moisture absorbing) tendency of RSG which can be an issue in humid climates.
RSG Recipe and Instructions for Sizing Stretched Canvas
- Measure 1 part RSG to 20 parts water, by weight (e.g. 50g RSG to 1,000g or 1L water)*
- Measure 1% allum by weight of RSG (0.5g or about a pinch for 50g RSG)
- Set aside a small amount of the water and dissolve the alum in it.
- Mix the RSG with the rest of the water.
- Let the mixture stand overnight
- Add the alum solution and heat the mixture gently in a double-boiler until the RSG has been fully dissolved. Do not allow the temperature to exceed 60°C (140°F) as this would reduce the glue’s strength.
- The glue can be applied warm to hand-mounted, not-too-tight canvas. Using a large brush, work vigorously using circular motions to ensure the glue penetrates the surface evenly. The fabric will tighten instantly and become even more taut as the glue dries. Watch out, this tension can actually tear weak or overstretched fabric and even snap poorly built stretchers! The larger the canvas, the stronger the tension therefore the less tight it has to be before being sized.
- Apply one or two more coats, allowing the surface to dry completely and sanding lightly between each application.
- Once properly sized, the canvas is ready to be painted. If you want, you can add a layer of gesso to change the strength, color and texture of the ground.
- The leftover glue will keep for a few weeks in the fridge and can be reheated when needed.
*RSG is a natural product and as such will vary in strength from one batch to another. You can test your glue by allowing it to cool down and gel after Step 6. At this point the desired consistency for canvas should be firm but friable, easily crushed between the fingers. If the gel is too stiff or too soft, you can alter the proportions accordingly.
- For sizing wood panels stronger glue may be prepared by increasing the concentration of RSG. On thinner panels, it may be advisable to size both sides as the tension may warp the board.
- For sizing paper for watercolor or ink a much thinner solution will suffice.
Simply put, gesso is paint that is applied to a surface as the final step in preparation for painting proper. The idea is to create a strong flexible ground that has the quadruple purpose of 1. further protecting the support from acids in the oil 2. altering the texture of canvas (or creating new, interesting textures) 3. providing a receptive layer for oil paint and 4. serving as a ground color. Although it is possible to paint directly onto properly sized support, the addition of gesso has many advantages in regards to archival and aesthetics.
Acrylic gesso is the most common gesso found commercially today. It is basically white acrylic paint mixed with calcium carbonate (chalk) and various chemicals. But given it’s short history, oil painters should do well to avoid it. Also note that almost all ready-made canvases sold today have been primed (sometimes very poorly) with acrylic gesso. If you are planning to use such supports it is probably sound practice to add at least one more layers of gesso to make sure that all the miniature fissures and holes are filled, because, in most cases, the canvas underneath has not been sized.
Oil gesso in its various mutations consists generally of an emulsion of rabbit skin glue and linseed oil mixed with chalk or stone dust and pigment (usually white). Painters of the past usually prepared this mixture themselves and adjusted it to suit their needs; varying the proportions to obtain more or less absorbent and more or less textured grounds. Gesso was usually applied in thin coats of alternating direction. The process of preparing and applying the mixture can be long and tedious, especially for large canvases.
Lately I’ve been experimenting with an simple oil gesso mixture consisting of Blanc de Meudon chalk and boiled linseed oil. Properly mixed and applied to sized canvas, this mixture can produce very nice textures and dries quickly (2 weeks or more depending on thickness) to fairly smooth finish which is easy to work on. This methodology completely breaks the age old axiom of ‘fat over lean’ As such, it is more of an ongoing experiment as I don’t know yet how it will fare over time. My bet is that, considering that boiled linseed oil dries very quickly, the gesso layer will dry completely before any of the subsequent paint layers do. If I lose my gamble, the situation will be reversed which will probably lead to premature cracking as the upper, drier layers are stretched by the still flexible gesso layer.
In any case, here is a quick recipe for curious painters. (I assume no responsibility if your masterpiece suddenly crumbles to colored dust!)
Boiled Linseed Oil* Gesso Recipe
*Boiled linseed oil, also sold as linseed oil varnish in hardware stores and by Kremer, is intended for use on wood as a protective coating (really nice, by the way) It usually contains drying agents and will yellow considerable over time. It is definitely not a good idea to use it as a painting medium, but for a gesso, it should be fine (again, no garantees 🙂 )
- Pour some boiled linseed oil in a mixing bowl and gradually add fine chalk (Blanc de Meudon, if you can find it), ideally sifted through a fine sieve, as you mix.
- Don’t mix too vigorously, to avoid forming to many bubbles.
- You may add a fine pigment of your choice (most likely titanium white), or even some paint directly from the tube (it’s probably a good idea to stick with fast driers in that case: burnt umber, mars black, ochers, ultramarine…)
- Keep adding chalk until the mixture is fairly thick and harder to mix but still runny and completely homogeneous (no lumps). The thickness point is really a matter of purpose and taste, but do bear in mind that the less chalk there is the more oil there is (relatively speaking) and, as such, the gesso will take longer to dry (for a given thickness).
- Apply with brush, palette knife, sponge or whatever tool any way you like. One can obtain very nice textures with a thick mix.
- Allow to dry for at least two weeks. This may seem like a long time but if you prepare a few canvases in advance, it’s really not an issue. Painters in a hurry can go buy pre-stretched, pre-gessoed, pre-botched, over-priced canvas if they like!
Traditionally, lead carbonate was overwhelmingly used as the white pigment in painting. Called lead, flake or Cremnitz white, it has many characteristics which make it an ideal choice for painting: it is transparent, fast drying, malleable and light-fast. However, during the 20th century, rising health concerns made lead less and less popular among artists and consumers. Consequently, the production and supply of the pigment decreased significantly; what is more, strict regulations in certain countries have made it very difficult to acquire. Under these circumstances, the modern alternatives to lead white are zinc and titanium.
- Zinc white has the advantages of being transparent. Sadly, a study by the Smithsonian Institute has raised alarming concerns as to its long-term aging properties. Artists concerned with the durability of their work should avoid zinc white completely.
- Titanium white, as far as I know, is a stable, lightfast pigment, however it also has the major drawbacks of being opaque and very slow drying. Used on its own, titanium can easily overpower weaker pigments, leading to chalky, pastel tones that take forever to dry. Luckily, there are workarounds. The addition of calcium carbonate (chalk, Blanc de Meudon) imparts transparency and accelerates the drying process. Corn starch improves the consistency of the paint giving it a stiffer, more sculptural impasto quality. To prepare my whites, I mix together walnut oil based titanium white paint with chalk and starch in varying proportions and a minimal amount of walnut oil. Each mixture is adjusted to suit my needs and the result is a high-performance, versatile white paint that comes very close to imitating lead.
Drying oils such as linseed, walnut, poppy and safflower along with pure pigments are the only two components in high-quality tube paints. When these oils come into contact with air they undergo a chemical reaction that progressively transforms them from liquid to solid. Each oil reacts differently, drying at different speeds, to varying hardness levels and aging in different ways, sometimes yellowing over time.
There are many options when it comes to oils. I err on the side of caution, and avoid modern inventions such as alkali-refined oils, sticking to time-honored products whose stability has been tested and proven over the long history of oil painting.
- Linseed oil is by far the most common vehicle used in oil paints today. It is easy to find, cheap and dries relatively quickly. However, the industrialization of the refining process has significantly reduced the quality of oils available to artists today, leading to oils that have may have a tendency to yellow over time (although some do not) and that produce a weaker paint film. It is possible for painters to refine their own raw linseed oil to produce a non-yellowing, fast-drying oil (see here).
- Walnut oil dries more slowly than linseed oil, but is less prone to yellowing. Although the quality has also been affected by industrialization, it is still a better option than most commercially available linseed oils. This oil, mixed with turpentine and sometimes walnut sun oil (see bellow) is my all-around painting medium.
- Poppy and safflower oils are said to be the most non-yellowing of drying oils commonly available. But they are also a very slow driers. For this reason, I have never used either one. Some cautious painters use these oils only for the lightest and brightest passages, to minimize the chance of yellowing.
- Sun oil refers to oil that has been left to thicken and bleach in a tray in direct sunlight for several weeks until it has the consistency of honey. It dries extremely fast to a hard, glossy finish. It also imparts leveling qualities to the paint, eliminating brush strokes. As such it is, in my opinion, the perfect glazing medium. I have even used it pure as a varnish. Sun oil may be bought, but it is usually extremely expensive, so curious artists should make it themselves.
Sun oil recipe
- Pour pure high-quality, cold-pressed, or home-refined, oil in a wide tray.
- Place a sheet of glass over the tray to protect the oil from dust and debris.
- Using a few matches or something similar, create a small gap between the glass and the tray to allow air flow.
- Place the tray next to your sunniest window.
- Agitate the oil every week or so to prevent the formation of a film on the surface.
- When the oil has the consistency of honey, it may be filtered in a cheesecloth to remove any impurities, bottled and is ready to use.
- Even once bottled, the oil may be stored in direct sunlight to further the bleaching process.
Solvents, or thinners, are mixed with paint to increase flow especially in the initial stages of a painting. They are also used in the studio to quickly clean brushes and palettes. On this point, bear in mind that their corrosive action, over time, will damage the delicate hairs of natural brushes (see below for a note on cleaning brushes).
- Turpentine is produced by collecting the vapors released by heating the sap of certain coniferous trees (traditionally the terebinth tree). Its long history and pleasant pine odor make it an ideal choice for oil painting. But remember that turpentine is an organic solvent, its vapor can irritate the skin and eyes, damage the lungs and respiratory system. However, used in reasonable amounts and in a well-ventilated space, most painters will have no problems using turpentine daily.
- Mineral spirits or white spirits and odorless mineral spirits are a modern alternative to turpentine. Their lower toxicity means they are a good choice for sensitive or health-conscious painters. One must still take precautions to work in well ventilated spaces as their faint odor could lead to underestimating their concentration in the air.
A note on cleaning brushes
Although most oil painters clean their brushes with a solvent and I do the same when I am in the act of painting, I have found that using a slow drying oil such as walnut oil to clean my brushes at the end of the day has the double advantage of being non-toxic and better for preserving the natural hairs and bristles. (For synthetic brushes, just solvent should be fine)
- Using a drill, make a bunch of small holes in a plastic jar lid.
- Place the lid right-side up at the bottom of a larger jar or metal can.
- Pour in enough oil to immerse the lid.
- Clean your brushes by working them against the holes in the lid. The pigment will dissolve in the oil, run through the holes and settle at the bottom of the can.
- Wipe off as much of the oil as possible from the brush hairs using a rag.
- Remember that the leftover oil on the hairs will dry out if a brush goes unused for more than a week. One should clean unused brushes with soap (Savon de Marseille is a good choice, but any soap should do) and warm water before reaching this point.
- The leftover pigment sludge may be cleaned out of the can every month or so and reused as a background color, for example.
Yet another option to eliminate the tedium of cleaning brushes altogether would be to devise a sort of inclined tray partway filled with a slow-drying oil in which the working end of dirty brushes could simply be immersed at the end of the day. It would then be a simple matter of twirling them in a bit of turpentine and wiping them off before using them again.