Note: If you're looking for Tad's PDF on oil refining, or his book, they're posted at the bottom.
When I first started researching traditional varnishes and oil finishes, one name that kept popping up was Tad Spurgeon. He's well known in the art world, but I suspect few woodworkers--with the exception of violin makers--have heard of him. His website is regrettably shutting down at the end of this month (9/22), so I wanted to give him a proper sendoff, and also post some materials (with Tad's permission) that readers can download and explore if they're interested.
Tad is a very accomplished painter, but he's perhaps best known for having almost single-handedly revived the ancient practice of washing linseed oil. You are probably wondering why on earth anyone would want to wash linseed oil. There's a long answer…but the short answer is that a washed oil dries in about half the time of raw oil, will yellow or darken less, and be far less susceptible to mold or mildew. So if you are using oil as a primary finish, or using it to make varnish or paint, your results will be better.
Spurgeon started washing linseed oil because he wanted to make his own paint. Today, most artists go to an art store to buy paint made in a factory, but before the 20th century, artists generally made their own paint. Unsatisfied with the answers he got from 20th century writers, Spurgeon turned to sources such as the 17th century De Mayerne manuscript, and to a pair of important 19th century texts by Eastlake and Merrifield. He found that prior to the 19th century, artists typically used cold pressed, hand washed oil to make paint and varnish their canvasses, and that many of the paintings had lasted centuries without appreciable darkening or deterioration. But in the 19th century, as the use of hot pressed, industrially refined (or unrefined) oil proliferated, darkening became common, and by the 20th century, artists' textbooks treated it as a given.
Over a period of years, Spurgeon experimented with the oil washing methods described in the older sources, and rigorously recorded his results. In some cases he was able to systematize older methods and make them more efficient, and he also developed some entirely new methods. He also explored--and again thoroughly tested and documented--related methods of processing such as heat treating, oxidizing, and aging in sunlight. All of this is laid out clearly and concisely in the Oil Refining PDF at the bottom of this post, and it's well worth checking out.
For woodworkers, the linseed oil research is the most directly applicable part of Spurgeon's work, but for him it was just the tip of the iceberg. In his book Living Craft, he reconsiders the totality of the painter's materials in the same vein, and seeks to reestablish a craft based on handmade materials, in sharp contrast to the modern practice of using purchased materials.
I'm a woodworker, not a painter, but Spurgeon's work has influenced mine in a number of ways. First, there's the idea that using handmade materials changes your relationship to the craft. As a toolmaker, this notion already had resonance for me--I've made most of the planes, floats, and other specialty tools that I use in my daily work. But formulating my own finishes out of hand-processed oils and natural resins added a new dimension to the work: Finishing becomes a much more integral part of the process, and one that has more meaning, when you're not just buying a bottle of mystery liquid at the hardware store and slapping it on.
Second, Spurgeon serves as a model for how to approach research as a craftsman, rather than as a scientist. His tests of materials don't pretend to be formal scientific experiments--and they're the better for it. Over the years, I've seen many attempts to do scientific tests related to woodworking--on finishes, on tool steels for chisels, on planing angles, you name it. They usually fall flat, either because the designers lack expertise in the craft, or because they try to remove any trace of the human hand, in a misguided effort to ensure objectivity. Building a machine to chop particleboard with a chisel, for example, may seem more objective than having an experienced woodworker chop dovetails in maple all day, but it's not very useful for telling us about the feedback the chisel gives the hand, about how difficult it is to resharpen, or how well the tool integrates into normal workflow. In a similar vein, tests on linseed oil that use advanced imaging or analysis methods may look impressive, but if the experimenter doesn't have real experience using and processing the oil, and just uses any old oil off the shelf, the test is likely worthless, because not all linseed oils are the same.
Which brings me to one of Spurgeon's most important insights, which is that many basic materials that we take for granted are fundamentally unlike their historical versions. Linseed oil is a great example, but there are many others…turpentine, for example. That noxious substance that you buy at the hardware store is so unlike traditionally made turpentine that it doesn't deserve to be called by the same name.
Spurgeon isn't the only one to discover this: In many ways, his thought parallels Michael Pollan's writing about food in The Omnivore's Dilemma, In Defense Of Food, and elsewhere. And that's not a coincidence. As Pollan shows, the industrial system of production that has developed since the late 19th century has fundamentally transformed our food, from flour and tomatoes, to chickens…and the same is true of linseed oil and turpentine. The food industry and the coatings industry are two sides of the same coin, and both are built, as Pollan might say, on the same, slowly sinking sea of cheap petroleum.
That's a depressing thought, but as Spurgeon dryly notes in Living Craft, we still have opposable thumbs. So, if you want to taste how different a real tomato is from the industrial crap at the supermarket, get a Brandywine plant (or some other heirloom variety) and grow it. And if you want to experience how different good linseed oil is from the crap at the hardware store…well, download Spurgeon's writings below, and get cracking.