Japanning

From roughly the mid-1600’s until about 1925, almost everything made of steel was japanned, coated with a mix of stuff that formed a fairly solid, waterproof, rustproof coating.
I recently repaired, for a local vintage computer/technology museum, their edison spring wind up record player, because the amplifier tube had broken. It was coated in japanning. Old wood planes and woodworking equipment was usually treated the same way, so if you have something older, it’s useful to know about.
Paint stripper takes it right off. Like, any type of paint stripper. Acetone, probably even gasoline.
The stuff itself is composed of 4-5 parts turpentine and 1 part boiled linseed oil. Mix these, and then comes the tricky bit. You add in asphaltum aka gilsonite, which is a solid, powdered, coal tar derivative. You can get this from art paint suppliers. I got about 500 grams off ebay. The thing that you don’t know starting out and I’m here to tell you is: it dissolves quite slowly, and you want a consistency about like honey or molasses, so what I found is that if you add in enough to get that consistency, over the next ten minutes it’ll go blazing past that consistency and have the viscosity of chewing gum.
So what I found that worked was: dump in about the same volume of gilsonite as the solvent volume, on a hotplate with a stir bar, and gently heat it, like to maybe 45C, with stirring, and as the overwhelming turpentine stench rolls off the jar, it’ll dissolve faster and produce the right viscosity.
It has about a 20 minute working time before it definitely begins to solidify.
Don’t use a brush (or for that matter a mixing cup) you care about much: this stuff is pretty messy and pretty tenacious even with use of turpentine to clean it up.
It will room cure but it takes weeks. Traditionally, people hot-cured it by putting it in an oven and heating it up to 200F, then letting it cool down, then up to 300F, cool, and 400F and cool. Those seem like awfully arbitrary numbers. I used a space heater with the amplifier horn in a box, and cranked it up to about 250F, let it cool down, then as hot as the heater could get the space (about 350F) and it came out pretty well: a hard, shiny, smooth, black coating that seems to be pretty tough.

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Japanning is quite fascinating to me as a metal finish coat. Hand Tool Rescue on YouTube does quite a bit of Japanning. Here’s a video he did on a basic history of Japanning and his best recipe.

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