Monday, September 5, 2022

The Search for the Perfect Finish

Turpentine trees, Florida, 1936. Courtesy: Library of Congress.

There is no perfect finish, of course. But the search for the right finish for the traditional wooden planes I make has turned out to be far longer than I imagined, and led to places that I never would have expected. Most surprising of all, it's opened the door onto a whole world of pre-industrial craft that I didn't even know existed.

 This month, I have an article coming out in Mortise & Tenon Magazine titled Reconstructing the Varnish Maker's Art: Traditional Finishes for the 21st Century. The article represents one strand of my journey: A deep dive into the history of traditional finishes, especially natural resin varnishes. So in this post, I want to give some background context, and shed some light on how I went from perusing the shelves at my local hardware store to poring through 17th century manuscripts and cooking resins at 600° F on a hotplate in my driveway.

My earliest planes had with simple oil finishes, but when I started making planes for sale, I realized I needed a more durable and protective finish. For a while I used Minwax Antique Oil, because it's popular among planemakers, but I quickly got tired of it. Like so many synthetic finishes, it looks plasticky to me--which makes sense, because the resin component is almost certainly some sort of plastic. And the application process is a pain in the ass. So I moved on, searching for something that would look better, and hopefully be a little less toxic.

For a while, I used polymerized tung oil, and that was okay. But you really need to sand between coats--tung oil never leaves a completely smooth surface. The resulting surface is matte, and I like matte, but this was a bit too matte even for me. So I felt like I needed to wax after buffing the last coat, and that was a pain in the ass too. Plus, you need to keep waxing or the matte surface returns, and over the long haul the tung oil seems to get more opaque.

One other thing I didn't like about tung oil was the way it feels, and that was a problem with the next finish I tried: Osmo. I was talking to Don Williams (renowned finishing expert and former Smithsonian conservator) about this, and he brought up the term "mouth feel," which is apparently used in the food industry a lot. I understood his point right away. I guess we could call it "hand feel," but whatever it is, I didn't like the way Osmo and other hard wax finishes felt. And while it's durable, it's not as durable as some of the other finishes I had tried.

The last commercial finish I used was Birchwood Casey Tru-Oil, and I used it for quite a while. It's a lot like polymerized tung oil, but because it's mostly linseed oil, it doesn't leave that rough surface. It's easy to apply, durable, and looks good, though the look was never quite what I was looking for. And it can dry a little too fast--using it on a hot summer day can lead to a lot of extra work, buffing and reapplying. But still, it was the best commercial product I could find, and I finished a lot of planes with it.

 Meanwhile there was a memory, more than 20 years old, that kept nagging at me. When I first started woodworking, I read a Fine Woodworking article about varnish. It said there were three main types of resin in varnish: Phenolic, alkyd, and polyurethane. I didn't know much about these substances, but I figured they were synthetic, and I wondered how people made varnish before they were invented. I finally started to get a hint of an answer when I happened on an article by the aforementioned Don Williams that pointed me in the right direction. Another phone call to Don followed, and pretty soon, I was doing crazy shit, like washing linseed oil…



and cooking things like Congo Copal resin…



to make real varnish that comes from plants and trees.


Many batches of varnish followed, and I had test samples strewn all over my shop. It's one thing to make varnish; it's another thing to make varnish that you'd rather use than any commercial product. You have to have a high tolerance for failure.Eventually though, I got to a place I was pretty happy with.

Here's a view of a test sample: Tru-Oil in the foreground, Copal varnish in the back. 



Here's another view, this time with Copal in the foreground.


The Copal is a bit darker, though the difference appears much smaller when viewed straight on. It's a lovely color, but what's more remarkable is the difference in reflectivity. With two thin coats of Copal varnish, the wood doesn't really look like it has a film on it; instead, it appears that the shine is coming from the wood itself. Which is what I was after all along.

Anyway, there is more in the Mortise & Tenon article, so have a look if you're so inclined. Yes, it costs money, but it's well worth it--there are many other terrific articles, and Josh and Mike do a great job with the visuals.

I'll have some more posts on the subject this month, including recipes and an interview with the guy who knows more about this stuff than anyone alive.



  1. Thanks for the info. Looking forward to the article. As an organic chemist and a woodworker, I've been looking for the perfect finish as well. Mostly I've stuck with shellac but recently I've been branching out into oils. Really looking forward to your article.