I use wood, Nowegian "stonebirch" with silver in bezels. And
plumtree and cherrywood. These are very hard. The patterns and
colors are amazing.
Wood is changing size depending on humidity if you dont protect it
with something really hard or something that goes all into the wood.
Its not easy if the wood is hard and old.
If you bezel them in larger pieces, you must pin/stick/glue them
with a couple of holes into the wood, through the bezel, because of
the change of size, its alive. If you only glue it, it will loosen
from metal over time.
Its not easy to make it jewellry quality surface, it requires lot of
sanding, and some sort of oil or wax. Or shellac, it makes a hard
surface, but may be not what you are out for. There are special
sanding papers made for woodcutters that are great.
Pipemakers have their own wax, it works for polishing. Use an old
wool sock for the last finish...OR if you are able to get it, real
untreated wool from sheep. Beezwax gives spots when splashed with
water or sunshine.
A sami man that use to make intarsia with wood teached me to throw
pieces into a closed jar of best quality vegetarian oil after they
are almost finished and sanded to the best, and let them lie there
until he wants them. They can stay for years. If you do, take them
out some days before you will use them, and let them lie in natural
cotton till they have given away some of the oil. Polish with wool.