The only material used is solid hardwood.

We have a 9 hectare elm - black locust forest. We
planted it when I was a teen. I actually cultivated it when it needed in the
first years. But that needs a few decades to be cut. My son can use that wood
in his thirties.

Until then I use exclusively FSC certified wood. I use
only EU domestic species; oak, beech, ash, black locust, maple, larch, pine. I
have never used exotic wood for any project and I never will. Heck, I also avoid
using walnut, since it has been overharvested in the 20th century. It
is, because its wood is dark and attractive.

But I know a much better choice for what I do. Fumed
oak is more figured and more durable (harder and wear resistant) than walnut and
it has narrower sapwood (the light coloured edge) than walnut. Oak is much more
sustainable than walnut because its plantations are tens of times more
widespread than walnut. Walnut can retire at last!