I’ve been exploring a wide variety of wood finishes suitable for wooden tableware since I started turning—I make wooden bowls and cups after all. Like wooden boats, woodenware has to hold up to extreme conditions. Maybe more so, as it goes through wide swings of swelling and shrinking aka washing and drying on a daily basis. That process is extremely hard on wood and the finish is there to slow or prevent it. Sometimes cups just can’t take it any longer and simply crack from rim to base. It’s a hard sell and part of the reason wood was mostly abandoned as tableware—at least in the West. There are more stable and predictable materials to use, like fired clay, metal, glass and plastic. But there is nothing like the beauty, texture, and warmth of wood, its quietness in use, and its closeness to nature.

The most common finishes in the green woodworking scene are linseed, tung and walnut oil. I’ve used all three with disappointing results. They all have a taste, a smell and a lack of durability. Washing wooden tableware with alkaline soap will degrade those slow polymerizing oils in no time. I’ve seen it first hand because I’ve used woodenware treated with these oils for over ten years on a daily basis.

The FDA’s food grade classification of resinous and polymeric coatings is diverse to say the least. Have a look here. It includes a vast range of finishes. You’ll have to freshen up on your chemistry to understand much of it. The short of it is that most, if not all wood finishes are food grade after they are left to cure for 30 days. That is to say according to the FDA after the 30 day cure time all these finishes are considered inert and can’t do any harm to us. Having said that, it’s still a controversial subject among some scientists. Nothing new there. If you haven’t figured this it out yet, there is rarely consensus in the world of science.

All of this considered, I’ve been exploring more mainstream finishes. Some hold up to use much better than the main three oils aforementioned. And they are tasteless. Currently I’m using the equivalent of German Osmo for most of my tableware, which pass food grade standards in the EU and the States.

This quest for the perfect wood finish has also led me to Urushi lacquer. It’s been in use for over 9,000 years and is possibly one of the best natural finishes for wood on Earth. I’ve written about it here. It’s a tree sap and 100% natural. There is a caveat, it’s almost entirely made up of urushiol so it requires training to apply and cure correctly. Once fully cured, it will last for 100’s of years. I believe it’s the main reason wooden tableware has been in continual use in Asia since the Stone Age. After our lessons on lacquer application in Japan three years ago we’ve been making lacquered woodenware for sale, with very satisfying results.

While in Japan I learned of another finish known as liquid glass which was tasteless, odorless, and had a very matte finish. In fact, the wooden items I saw appeared not to have a finish at all, and yet still beaded water on its surface. I was obsessed. Back home I spent months searching for more information. If you search liquid glass on the internet, what comes up is either an epoxy or nano finish. But that’s not what the liquid glass I knew was. Unfortunately most internet searches of Japanese terms are lost in translation due to how complicated Japanese written language is. They have 3 different written language systems—kanji, hiragana, and katakana—and you may see a combination of all three when looking at a simple food label in Japan. Added to that, translating something with highly technical language can be especially difficult because some of the kanji is so specific and uncommon that even a Japanese reader may not understand it. All this to say I had a difficult time finding out more information on this mysterious liquid glass.

Tokunaga in his studio with a couple of his signature chairs. ©2019 Woodspirit Handcraft — Tokunaga in his studio with a couple of his signature chairs.
©2019 Woodspirit Handcraft

My friend Masashi introduced me to Toshio Tokunaga, a highly respected furniture maker in Miki City, Japan. I wrote about our visit here. Tokunaga’s chairs are amazing. A signature part of his work are the elegant curves in the chair parts—arms, legs, and backs meeting in a harmonious balance. And each of these parts is worked with a tiny hand plane that Tokunaga developed himself in order to get a glass-like finish regardless of the wood’s shape and grain direction. The visual appearance and more importantly the feel of the chair’s surface when touched would not be right under a layer of polyurethane or other common finish that would cover the surface of the wood. Because of Tokunaga’s strict standards he began looking for a finish that would protect the wood, but not compromise his desired finish. The matte finish of liquid glass which lay under the surface of the wood met his approval.

The whole story is not completely clear to me, but what I understand is that he ended up helping develop a specific brand of liquid glass called Hassui Ceramic Coating with the Hassui company, one of many companies producing this type of finish in Japan. We were able to meet with a Hassui representative at Tokunaga’s house and talk about the product. They seemed very interested in promoting this product outside of Japan. Back home, Austin Voll, a student of Tokunaga, helped us get our first sample which we tried out on a run of shrink pot tea canisters. We felt that this finish had great potential and through negotiations managed to import a large sample can from Japan, both to use ourselves and to share with other woodworkers.

What is it? The coating is made up of molecular silicon (Si) suspended in alcohol. (Don’t confuse Silicon with silicone!) When applied to wood it is absorbed into the surface, the alcohol evaporates and the silicon bonds with oxygen in the air and the moisture in the wood to form a type of SiO bond which is glass. It is not a nano coating, those are a completely different type of finish being developed. I have to admit that learning the true chemical nature of this product is hard won. I learned more about chemistry than I wanted. Once it has vitrified and the SiO bonds are complete it is inert and food safe. This takes 2-4 weeks. Although it is dry to the touch after just a few hours. Those glass bonds are actually within the surface of the wood, coating the wood’s fibers and cells. After curing, a splash of water on the coated wood surface simply beads up. To demonstrate the process I was told to set a few teaspoons of the finish in a plastic cup and wait for the alcohol to evaporate. After a few days I checked on it and sure enough the liquid had turned to glass in the bottom of the cup!

Stool with Hassui Ceramic finish, Dawson Moore ©2021 michigansloyd.com

This finish has amazing possibilities, especially for furniture makers and high end woodworking. It highlights any knife or blade finished surface. Currently Dawson Moore of Michigan Sloyd is using it on his chairs and stools and seems pleased with the finish. It passes Japanese food safety standards and can be used on wooden spoons, bowls, and cups. I’ll be using it on the knife handles that I’ll be making. It’s not good for cutting boards because the glass will dull the knife blade. We even used some around the sink on our wooden counters and painted it behind the stove in place of a backsplash.

To promote Hassui Ceramic Coating we are offering a limited quantity of 4floz sample cans for sale at a discounted rate. Samples ship UPS Ground to US addresses only (no PO Boxes) and can’t be combined with other products. As far as I know this is the only place you can buy this outside Japan. If there is enough interest we’ll explore importing larger quantities. The sample cans come with a second inner lid to completely seal the volatile contents. Use a box cutter blade to pry the inner seal open, but keep it to replace afterwards to prevent the liquid from evaporating. 3 coats seem to work well, applied with a brush that cleans up with rubbing alcohol. It’s dry to the touch within a few hours, but we usually wait a day between coats. The complete curing/bonding takes a couple weeks. More than 3 coats may create glossy areas on the surface of the wood which you may or may not like. Wiping the wet surface between coats will even out the finish. Depending on the pores of the wood you are sealing, the first coats of the finish use up more product and may be hard to see as it soaks in. Successive coats use less product and dry faster. Use gloves, provide ventilation and follow all directions on the label for safe handling.

We hope you enjoy trying out this finish! Let us know how it works for you.

The product is known as Tatara in Japan.

Visit HASSUI CERAMIC USA for more information on ordering Hassui Ceramic.

Hassui Ceramic Coating from Japan aka Liquid Glass

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