20% Boiled Linseed Oil
My translated recipe to make 8 ounces
4 ounces Turpentine
2.4 ounces Asphaltum
1.6 ounces Boiled Linseed Oil
As usual, I was shocked at how impossible it was to find an actual reproducible recipe. Sure, 19th century manuals and reference books have various recipes but those recipes include archaic measuring systems and toxic additives.
It wasn’t until one my favorite YouTube channels, Hand Tool Rescue, finally showed a working recipe that we had something usable. I’d been researching this process for some time and am happy to report that this is a great recipe and is an easy to produce an incredibly durable period finish.
So, what is japanning? It’s a very old baked paint finish. Think of it like an old-school powder coating finish. It was so popular and durable that early Ford cars used the finish. If you’ve ever picked up an antique painted tool that has survived the test of time, odds are it’s because the paint is japanning.
Japanning’s durability comes from the asphaltum which is dried, powdered tar. You can buy it from a few art supply stores or Ebay. It is very dry, very fine, and easily makes a mess, so you’ll probably want to use gloves and a mask when mixing it. The asphaltum dissolves in the turpentine over the course of about 24 hours. The baking process speeds up the curing and hardening process.
Adding asphaltum to paint formulas was common throughout the 19th and early 20th century. Japanning involves a baking process, though cold formulas also existed and were commonly used and recommended for exterior finishes and coating metal. A modern cold recipe simply involves mixing a 50-50 ratio of asphaltum to a good spar varnish and allowing it to dissolve and mix thoroughly. Whatever the formula, the major protectant was asphaltum.
Making the japanning mix is fairly simple, though you do want to try and be as precise as possible. It can be tricky translating percentages into measurable amounts. This mix goes a long way so I didn’t want to make a ton of it. This 8 ounce recipe should last you quite a while if all you do are small projects like buckles, tin cans, or an occasional hand plane.
I used my postage scale to weigh the ingredients before adding them to a metal, pint-sized paint can I purchased from Home Depot. Using mason jars are also common. I recommend using a plastic spoon to measure out the asphaltum carefully. Once all the ingredients are in the can, stir thoroughly, replace the lid, and allow to dissolve for at least 24 hours. After the waiting period, stir very thoroughly again prior to application. I recommend using some form of degreaser like alcohol prior to application.
This “paint” is odd. It’s like paint but has a syrupy consistency. Light coats and close observation are important on your first go. Also, if this is your first time and you need to japan something important, practice on another item first.
Once painted, it’s time to bake your pieces. I chose to use a $20 Walmart toaster oven that is dedicated to shop-use only. I don’t recommend doing this in your house or baking it in anything you cook your food in. I did this in my shop and it smelled mostly like turpentine with the faintest hint of tar.
There are some varying thoughts on bake times, but I baked for 1 hour at 250 degrees Fahrenheit, let it cool completely, then baked for another hour at 275-300F. It’s ballpark in my case because a $20 Walmart toaster oven doesn’t have a precise temperature control. The important thing is to not bake it too hot. When round two is complete, take it out and let cool and finish curing. This varies depending on climate and temperature. It’ll be dry to the touch pretty quickly thanks to the baking. However, for it to get it’s true rock-hard finish can take a bit of time. The finish is beautiful, glossy, glass smooth, and very black.
I want to close with a musing on curing times. In case you don’t know, there is a pretty big difference sometimes between an item being dry and being cured. Dry means it can be handled more or less but curing marks the completion of chemical processes in the products you were using. Think about it like bread going stale. You can easily move and handle it fresh, but it’s soft and a swipe of hard butter could rip it easily. If you leave it on the counter for a few days, it’ll get hard as hardtack. The bread going stale is kind of like the curing process.
I see a lot of people in the hobby bemoan the time it takes for things like linseed oil to cure as if it’s some major life hassle. I get it, we live in an a culture of instant gratification, but the people we research and portray didn’t. These recipes worked for them even with the “unbearable inconvenience” of curing times. The recipes were familiar to them, they worked well, and their schedules were built around the realities of the products they used. It didn’t take “forever” to them, it simply took as long as it took. Modern makers tend to feel they need to rush things. For me, dabbling in 19th century chemistry teaches me about period formulas and what the results are actually like. They also teach me about the patience and timing of life of the people who once used them. Remember, living history, is just as much about the process as it is the result.
I hope you found this article helpful and please feel free to share it. We just ask you let people know where you found it. Oh, and don’t forget this recipe contains boiled linseed oil so please dispose of your rags safely!