Here are some simple 100mm coasters, made from off-cuts of oak floor boards.
For the first ones I used a black acrylic paint pen to highlight the letters, sanded off the excess then oiled the whole thing. Unfortunately, despite a coat of varnish before the paint, and leaving it the black paint a couple of days to cure, the oil softened the paint and it bled
For the second attempt I used some Decorum epoxy resin pigments that my wife had given me for Christmas instead of paint. Learning from my first attempt, I brought the epoxy into the house to warm up, which made it more runny and allowed the bubbles to settle out. There are still a few little bubbles - is there any way (short of a vacuum chamber) to prevent them?
I also under-filled the larger letters slightly, so they didn’t get scratched when I sanded off the excess, but this didn’t work for the small letters (the grooves are only about 2mm across). Is there any way to keep the nice glossy, translucent finish? Or a way to get the epoxy in there that doesn’t require sanding afterwards?
Another thing I learned from last time was to engrave a circle around the outside of the coaster with the V-bit. I can then use this to as a guide to cut it out with a band saw, rather than risk a tool change.