Painting mediums are a never-ending topic for
discussion and debate among artists. Mediums profoundly affect how oil paint handles, and many preparations are complicated or dangerous, filled with ancient lore and alchemical processes.
Oil by its nature is flowing and slow drying, qualities that during the early Renaissance led to the birth of large-format paintings on light, portable supports. But by itself oil can be too flowing, so from the beginning, artists doctored their oils to speed drying and reduce flow. By controlling flow and drying time, artists hope to find that magic elixir that enables both the broadest effects and the finest detail–seemingly incompatible qualities.
While there is no single best medium, the one I use is flexible and well suited to my needs. The medium I use today is the result of many, many trials and tests. I have always wanted a medium that:
- flows under my brush and never interrupts my thoughts by sticking
- because I frequently over-paint, the medium must be as thin as possible but stay in place without running or sagging
- drys as quickly as possible without ever being sticky
The following describes –roughly–what I use (I say ‘roughly’ because I change proportions but this is a good baseline):
- linseed oil, 1 part
- copal varnish, 1 part
- turpentine, 1 part
- Courtrai drier, drops
Linseed oil. Because I want a very drying medium, I use black oil. Black oil is made by cooking the oil with lead driers. Black oil can be made at home or obtained commercially. You can substitute other drying oils. What should be avoided is thick or sticky oils such as stand oil. Walnut oil works just as well as linseed, by the way. You can also use regular or cold-pressed oil if you find the recipe too drying.
Copal varnish. Copal varnish drys hard and, compared to other resins, matte. Its dry, matte, finish supports frequent over-painting, and if the result is too matte, can be corrected by the final varnish (which is one reason to apply a final varnish). Copal varnishes differ from one another and if your varnish is oil-heavy and thick, you can decrease the amount of linseed oil in the recipe, or increase the amount of turpentine (or do both). Note: copal is a natural-occurring resin but many varnishes and mediums called ‘copal’ are made with synthetic resins. Try to get real copal.
Turpentine. Any artist-grade turpentine will work.
Courtrai drier. Courtrai drier is a powerful lead-based drier. A few drops are sufficient. Lead-based driers provide their powerful effects without making the paint sticky–an important consideration. It also firms-up the paint and enables thin paint layers, so don’t skip this ingredient. You can substitute other driers, but to see this medium to good effect, get yourself some Courtrai.
This recipe produces an excellent, and flexible, day-to-day medium that can be created without having to heat the ingredients together.
I use it every day but experienced artists will quickly spot its one limitation. If you are working on a large area that needs to stay open for a long period, like all day, this medium is too drying. Large areas will begin to close (the brush starts to drag) too soon. For these situations, I add a small amount of cold-pressed linseed oil (not black oil) to the medium to correct its super-fast drying speed. In the same way, you can add thickening agents, such as stand oil, for certain effects. It’s very flexible, like I said.
You can also slow drying time by treating the turpentine with a small addition of balsam, such as Venice Turpentine, or Canadian Balsam. I described the procedure in this post.