My painting medium consists of oil, essential oil (turpentine), copal varnish, and driers. I like my medium, and it’s suitable for everything painting-wise except a few corner cases. For the corner cases, I add a small amount of this or that, depending on the case. I like my medium, and I’m happy with it, but I’m always willing to try new things.
James Groves, that inestimable varnish maker, supplies two ingredients in my medium: copal varnish, and Courtrai direr. I’ve tried most of Groves’ products, and while not all are suited to my taste, they are all high-quality products.
Groves claims that the recipe for Cole’s Copal Varnish is based on the medium used by Thomas Cole, the 19th-Century Hudson River School painter. As with nearly all of Groves’ products, James provides a wealth of information about the varnish: how the product is made and how to use it. His literature for this product is long on examples but unusually terse on technical details.
With Cole’s Copal, Groves now sells three copal varnishes. His 19th Century Copal Varnish, an oil-based varnish (some varnishes, such as the ubiquitous Damar is resin and essential oil), is derived from old recipes, as are most of Groves’ products. This is my favorite varnish. His 19th Century Drying Copal Varnish is the same varnish with added driers. It too is excellent, but because I add my own driers, this varnish makes my medium too tight unless I modify the recipe. The last time I ordered varnish from Groves, he sent me this product instead of the one I ordered–19th Century Copal Varnish.
He also produces several copal-based painting mediums. You might be wondering what the difference is between mediums and varnishes? Oil paint is thick, slow-drying, and difficult to manage. A medium is a substance used to make paint manageable. It might be something as simple as oil and turpentine, or it might be a complicated concoction composed of several ingredients. A varnish, of course, is a substance used to protect furniture, musical instruments, and finished oil paintings. Varnishes are also frequently used as ingredients in mediums.
I’ve tried several of Grove’s mediums but I am wary of relying on commercial mediums, and I prefer to make my own.
Cole’s Copal Varnish is something of an anomaly. Groves expects his varnishes to be used as ingredients in mediums, but he expects users to treat Cole’s as a standalone medium. He warns users not to mix it with other ingredents except thinners. Used this way, it’s a good medium; slightly more covering than my normal medium. Of course, I also had to use it as an ingredient. Like a fool, I substituted Cole’s for my usual varnish. When I did, the studio wall blew out and fire scorched my hair. Just kidding. As an ingredient, it has a slight jelling tendency in the medium cup but otherwise handles OK. I still prefer 19th Century Copal Varnish. But I do like its covering capacity so I will keep a bottle of it in my kit for one of those corner cases.
As with his other products, Groves provides a wealth of demonstrations (no videos), which is excellent marketing for his products and his paintings.