I often infuse various types of Japanese green teas. High grade teas are usually steeped several times, using different amounts of water and temperatures at each infusion. For this reason I wanted to create a marker that would allow me to keep track of the infusions. This could prove particularly useful in tea-tasting sessions, where multiple teapots can be in use at the same time to compare different types of tea. In this scenario a marker for each teapot would make it much easier to keep tabs on the infusions. I made several prototypes and toyed with many ideas. At first I 3D-printed with PLA several variations of tiles, of various sizes, some of which could be stacked and even clicked together like construction blocks. Each tile had a number, from 1 to 5. I knew I wanted the final result to be wooden, but 3D printing was the fastest method to prototype, at least as far as my skills and tools arsenal go. The tiles felt cumbersome though, as those not in use would need to be scattered, maybe face-down, or they would need to be stacked in order. The final result is instead a single tile, with a marker bead that can slide under the numeral markings, as can be seen below. This provides a more clean experience, without too many loose parts.
Raw Material
For the raw material I didn't use anything particularly fancy. The original Yakisugi process ( 焼杉, literally "Burning Cypress"), used for house exteriors in Japan, calls for Japanese Cypress (Chamaecyparis obtusa) wood. This is a soft wood, so I decided to get something soft that was more readily available, in my case pine. I started from a short tile, 4mm thick, where the surface had been already leveled and sanded smooth. As a matter of fact the first prototype was made from wood recycled from a frozen prawns tray!
Marking
For the marking of the 5 symbols I printed a template on regular paper and glued it to the wood with PVA. This helped to keep things aligned and regularly spaced.
I then proceeded to score the numbers on the wood, creating thin lines, barely scraping the surface using a small rotary tool with a small attachment. I then switched to a conic tool to widen and deepen the markings, till roughly 1 mm deep. The lines between the numbers where instead scored with a jigsaw in a single pass to keep them straight and shallow, rendering them very subtle in the final result.
I then moved on to washing away the paper with lukewarm water. While the PVA and the paper came off rather effortlessly, in the following charring step it became clear that some PVA had been absorbed by the wood. This caused some bubbles to form during the charring. Sanding the charred surface lightly and repeating the process got rid of them. For a future iteration it would be worth trying to print the template on adhesive paper and drop the PVA completely. It's crucial to be really quick and not use too much water while washing. The wood will absorb water very quickly and, if you have been washing only one side, it will warp. I also carved two dimples on the short sides, towards the bottom of the numbers, using a small round file. These will keep in place the string that serves as a guide for the marker.
Charring
Before starting the charring process I left the wood to dry overnight as it had been washed. I then used a gas torch on a medium setting and proceeded to burn the surface until lightly charred. In a previous attempt I used a candle, but this seemed to only deposit sooth on the surface and produced no charring. I also, in a previous attempt, burned the edges too heavily. This gave the final piece an excessively accentuated and irregular rounding for my liking. Depending on the effect desired it could be a valid technique though. It is to be noted that especially edges catch fire very easily. Once they do blowing won't put them out, in fact the smoldering will move very fast along the wood. It's best to use a bucket with some sand or the edge of a plate to put out the fire. Water is an option but will require drying before more charring can be done so it's not very practical. From experience what works best is to leave the flame on a spot until charred and then move to an adjacent location. This will char much faster as it has been drying out and heating while the previous spot charred. Moving quickly the flame all over the surface can result in no or very slow charring depending on the flame and wind.
This is the result after charring the first two numbers.
Brushing
Once all sides and edges are burned the next step is brushing. For this I used a metal and a plastic brush. I first removed the coarse charred layer with the metal brush, without applying too much pressure as to not scrape the lower layers. I then proceeded to polish the surface with the plastic brush. A word of caution: in a first attempt I used a brass brush. Due to the softness of the material this actually left a brass coating on the wood. Make sure the brush is made of steel. Below is the result after brushing with the steel brush.
The two photos below are after brushing with the plastic brush, cutting off the excess and charring the last edge.
Oiling
The last step of Yakisugi is oiling. Linseed oil is traditionally used in Yakisugi for Japanese houses. The oil not only helps to protect the wood but it also gives it a finish that accentuates the natural wood grain. I made a previous prototype and found the smell of linseed oil rather off-putting. Given this is an item I'll be using when brewing teas I didn't like the idea. For the final prototype I went for a mixture of linseed oil and melaleuca oil. The choice was nearly accidental as the oil is also known as "tea tree oil" so I looked into it as I thought it to be connected with tea. I soon learned this has nothing to do with the actual tea plant, but I liked the smell and overall it worked very well for this piece. I went for 10 ml of linseed oil mixed with 15 drops of melaleuca essential oil. I then poured it on the wood surface, after making sure the piece was sitting horizontally on a generous layer of kitchen paper. I then left the oil to absorb in the wood for a good 10 hours overnight. I then proceeded to do the same on the other side and left it for 10 more hours.
Finishing
To finish it off I polished the surfaces with kitchen paper until they lost the greasiness. I then passed a length of polyester string into a bead that will serve as the marker. I finally assembled the marker as can be seen below.
By trial and error I found that it works best to measure the needed string length, then tie the knot at a slightly shorter length before actually mounting it on the wood piece. It's then a matter of pulling the string hard enough and let it sit into the two dimples. This will result in a comfortable tightness that prevents the marker bead from sliding on its own.
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