Actually I have used both linseed oil and tun oil, tung oil is much better. However to take care of your boken you need to sand the blade on ocassion. It sounds like your teacher doesn't know much about bokens. You need to get yourself a variet of differing sandpaper. Coarse, medium, and fine will do really. After you use it use the fine sand paper on the blade, then oil it, every time. If you have one of the cheaper red oak, thats covered in varnish, they do that for a reason. It's so the wood does not dry out, get brittle, and crack. It amazes me bhow little knowledge there is on here about something so simple. Anyhow, get a 3 dolloar sanding block, it will have a grip, rubber on the other end, and clasps on both ends to clip the paper on tightly. You only need to sand it to remove and of the raised areas, do not voer sand. You want the dents to remain, they are areas where the wood has compressed without seperating from the surrounding grain. However the raised edges aruond the dent, if any, have, abnd need to be sanded away, or the could become chips, and cracks, which can lead to the wood breaking. I have bought 12 dollar boken that, proplery maintained, lasted a student for 200 hours of sparring and still had not broken. However this is not true of all bokens, however, with proper maintenence your boken will last many times longer. Just remember, don'y over sand, always oil after sanding, and take good care of it. Hope that helps, and stay away from the linseed oil. Oh, and you can find tung oil in the paint section of home depot. Good day.