Liquid Glass Wood Finish – Update

It’s been close to a year and a half since I first posted about liquid glass wood finishes that are common here in Japan, and since that time I’ve been consistently using one finish in particular on wooden bowls and plates, some of which I’ve been testing out personally to see how the finish holds up. So far my experience is limited to using Tatara Hassui Ceramic, but there are many other liquid glass finishes (available only in Japan to my knowledge), so my experience is far from comprehensive. I hope to simply share some of the issues and trouble shooting I’ve done in regards to using this particular brand of liquid glass.

Initially I was really excited about Tatara Hassui Ceramic which I thought would solve a lot of the problems one encounters when it comes to finishing wooden tableware, and while I still think it’s a great alternative to oils, oil/wax mixes, or urushi, it’s definitely not a perfect finish. Overall my results using the finish have been somewhat inconsistent. In some cases pieces that I’ve coated with Tatara have worked out fine with no issues up to this point, but others haven’t faired so well. Determining what makes one piece a success versus another a failure has been a challenge. Assuming one follows the directions according to the manufacturer, my best guess is that successfully using this finish involves taking into account the species of wood, the grain direction and thickness of the finished piece, and the time allowed for the finish to cure.

Of those factors I’m starting to realize that a long curing time is a major contributor to the results you will get using Tatara Hassui Ceramic. The manufacturers instructions in Japanese for this product are as follows:

Separately there is a sentence at the bottom of the instructions stating:

漆に似た特性があり、2～3 ヶ月を目安に時間が経過すればするほど、結合性能が上がります。

Which more or less states that, like urushi lacquer, over the course of 2-3 months Tatara Hassui Ceramic will form a stronger bond with the wood.

It’s unclear to me what is exactly what is happening to the finish as it cures, or how it’s bond to the wood and overall strength and durability change. But I will say that after testing out a several pieces coated with this finish I’ve found the longer I wait the better. Even though the manufacturer states the finish will be fully cured in 20 days I’ve found that time to be somewhat insufficient. Washing several cups and bowls that were coated and allowed to dry for 20 days, quickly developed a dry and washed out appearance on the surface of the wood. But when taking a bowl and a couple plates that were coated 4+ months ago, and doing the same sort of washing test, I found that those pieces were far more resilient, and their overall surfaces and finishes still look great even after several heavy rounds of washing. Which leads me to believe that the longer you can give the finish to cure the better, and in many ways 20 days for a full cure doesn’t seem like enough.

Prior to realizing that longer curing times resulted in a more durable surface I ended up with a few test pieces that quickly looked washed out and dull after a few use/washing cycles. Which got me wondering what options there are for rejuvenating the surface? One solution is to apply another coat of Tatara, but that’s not a terribly user friendly solution for customers who may not have access to the product. For one cherry test bowl my solution was to apply a raw linseed oil/wax mix. The oil/wax was super easy to apply, required hardly any product, and instantly the surface of the wood looked rich once again. In fact the surface of the wood has stayed looking nice since I applied the oil/wax and that was over a year ago, and has been followed by frequent use and washing. I would have thought that any oil and wax would quickly be washed off from the surface but that hasn’t seemed to be the case.

My thinking is that perhaps Tatara does a good job of soaking into the wood, protecting and sealing the wood at a deeper level, while a surface coat of oil/wax can act more as surface protection. On the other hand, Tatara is really expensive and if ultimately it requires an application of oil/wax to keep a piece looking decent does it really make sense to continue using it?

Another issue I’ve encounted using Tatara is in regards to cups and bowls designed to hold liquids. My bowls and cups are all cross grain pieces so the end grain is exposed on two sides. Tatara initially provides an awesome level of water repellency, but in some cases I’ve found that just one washing with standard dish detergent has killed that effect allowing water to penetrate the wood and in the worst cases water leaks straight through the end grain. I will say my bowls are pretty thin walled, and leaking is perhaps less likely with thicker forms, but either way if water is easily soaking into the grain, that’s not exactly a good situation.

Here’s one birch vessel that was coated approximately 2 months ago to illustrate the issue.

I took the above vessel and washed one half of the inside with a soapy sponge (since it’s a cross grain vessel I focused on the end grain on one side of the bowl). I used a light amount of basic dish soap and only the soft side of the sponge, so I’d say the amount of washing I did was relatively light… in other words I didn’t go crazy scrubbing the surface.

The result on the non-washed side is visible below. No water seeping through.

But things are not looking so good on the side that was washed:

Soap seems to easily permeate the Tatara allowing water to readily seep through the end grain.

For cups and bowls the primary woods I use are cherry, maple and birch, and I’ve made a point to stay away from using more open grained woods especially with thin walled vessels. But even so I’ve had leaking issues with several pieces when the wall thickness was less than 3mm.

When the leaking issue popped up I started heavily perusing the Tatara Hassui Ceramic site for any information I could find about using the finish on wooden tableware, and I was especially focused on it’s use for holding liquids. Unfortunately there’s not a lot of information on their site, and when it comes to wooden tableware they more or less state that it’s up to the individual maker to do their own testing to see how the finish performs. But more importantly is the fact that they do clearly state on the website that Tatara Hassui Ceramic is not a waterproof finish, it’s just highly water resistant. I think I had glossed over that fact in the past given the number of people I’ve seen using this finish on wooden tableware. After looking at other liquid glass manufacturers I’ve found that they are all pretty similar in their characteristics, and they’re all highly water resistant but definitely not waterproof coatings.

In any case I’ve been experiementing with a few ways to deal with the leaking issue. My first attempt was to simply apply more Tatara. Usually I apply two coats of the finish, heavily saturating the surface until it just starts to stop soaking in. Doing so really uses up a lot of product so I had hopes that two coats would be adequate. To test out whether more coats would improve performance I took two cups which initially had 2 coats of Tatara (with 20 day cure time), and both leaked after washing with soap/water. So I recoated each cup 2 more times for a total of 4 coats on each cup, and again waited 20 days or so before testing them again.

Here’s one of those test cups made of birch with a iron acetate stain hence the dark color. It has a wall around 2-3 mm thick where the initial leaking was most prominent.

This one has a slight crack in it that showed up while turning which is why I kept it for my own testing purposes. The crack is obiviously unrelated to the perfromance of the Tatara, however water, or in this case hot tea, does seep through. The surrounding end grain, which previously leaked like a sieve, has eventually stopped leaking since applying the additional 2 coats of Tatara.

For comparison here’s the opposite side end grain, with no leaks whatsoever.

I’ve been using this cup fairly regularly since recoating it, and overall it’s been alright, but not perfect. Initially I would notice liquid seeping through, but over the course of a minute of two those leaks would slowly dry up, perhaps as the wood swelled a bit. After using the cup many times to drink hot tea those small leaks have mostly disappeared. It seems possible to me that sediment from the tea may also have helped plug up some of the pores as well. In any case more coats of Tatara did seem to reduce leaking, but didn’t stop it completely.

The crack even stops leaking after a minute of two as you can see below.

Here’s the other test cup that leaked pretty bad after I washed it with soap the first time. Now after recoating with Tatara it has been leak free. This test cup is from another variety of birch with a finer grain than the above cup, which is quite possibly a factor in it’s better performance.

So what about subsequent washing? So far things look good. I’ve washed these cups the same as before with a mild detergent and no leaks have developed. Perhaps the problem is simply that I failed to coat theses pieces adequately the first time, or should have waited 3-4 months to use them instead of 20 days as per the manufacturer? Up to this point I’ve certainly tried to heavily saturate the wood when I’ve been applying liquid glass, and the wood definitely soaks up a lot of product. But being a rather expensive finish, having to apply a crazy amount of it to achieve useable results on cups and bowls is a bit unfortunate. Also while the cups and vessel pictured above have leaked others have not, which is another head scratcher. I’ve pondered a lot about whether the problem comes down to the species of wood, quantity of product, or curing time, but the only thing I’m clear on at this point is that I can’t 100% trust a cup/bowl will be leak free when using Tatara Hassui Ceramic.

So I’ve also started digging into other options and other finishes. Another common finish used here in Japan for wooden tableware is called Kigatame Ace (木固めエース), which is essentially a polyurethane kind of product. It’s been designed to be foodsafe and is even used to finish bowls for use by children at schools in the prefecture where Kigatame Ace is manufactured. Kigatame Ace is essentially an undercoat, which being super thin, soaks into the grain hardening and protecting the wood. A lot of people follow it up with additional coats of sprayed on polyurethane, which makes for a really durable coating, but that also comes with it’s own downsides and challenges, one of which is the more plasticy feel and look of the finish on the wood. At a craft fair last fall I met another woodworker who told me he was coating his cups and bowls first with Kigatame Ace and then liquid glass on top of that. That led me down another rabbit hole trying to find out more info on the compatibility of the two finishes. After doing a lot of digging I found a short paragraph in a document on the Tatara Hassui Ceramic website stating that testing showed good compatibility between kigatame finishes and liquid glass. So I decided to give it a go.

I turned a few more cups to test the new finish regimen, and started by coating each of them with Kigatame Ace. The finish itself is really easy to apply. It’s essentially the same as applying liquid glass; it’s water thin and readily soaks into the grain. The main downside are the gasses and fumes. Kigatame is definitely not a finish you want to use without a respirator and good ventilation. I’m far from a fan of using finishes that smell like death, but given the situation decided to test Kigatame out nonetheless.

I tested a couple of cups coated with one coat of Kigatame Ace by washing them with soap and water, and then filled them with water and let them sit. The good news is that I had no issues with leaking whatsoever, even letting one of those first cups sit full of water for most of a day with no sign of water soaking into the grain at all. And that was again using birch with a super thin wall thickness between 1-2mm. (FWIW the manufacturer of Kigatame Ace states the finish is not waterproof, only water resistant, but so far it’s proven to be functionally waterproof from the testing I’ve been doing.)

In the meantime I also did a simple test with some Kigatame Ace and Tatara to test their ability to bond together. I put a small pool of Kigatame in a plastic container, let it dry, then I put another small pool of Tatara overlapping the Kigatame. Both finishes stuck to the plastic container and both bonded to oneanother as well. It’s far from a thorough test but I saw it as confirmation at least that the two finishes will stick to oneanother and don’t appear to have any negative interaction.

So with Kigatame looking promising I moved on to top coating with Tatara. The first thing that was instantly clear was that the wood soaked up far less Tatara than before, and with just one coat of Tatara, I found myself having to wipe the surface clean of product that wasn’t soaking into the wood. So Kigatame seems to do a decent job of not only making the wood much more water resistant (if not waterproof) but also cuts down the quantity of expensive liquid glass required which is a bonus. Also, the appearance of the cured Tatara over the Kigatame seems to just be a touch more shiny compared to using Tatara only. It’s a bit more noticeable that there is an actual coating on the wood, compared to straight liquid glass which can leave the wood looking raw.

So that’s my current approach to using Tatara Hassui Ceramic. I still think it’s an interesting product and alternative option for wooden tableware but working through some of these issues has definitely been kind of a pain in the ass. It’s also frustrating to have to wait several months for a piece to cure to a level that seems adequate before handing it off to a customer. Overall I have had good luck with the finish on plates and trays, and recently even finished some maple stools with it as well. But cups and bowls that are designed to hold liquids have been a challenge. I’m curious to hear what others have experienced as well, so if you’ve been using this finish let me know what you think.