Silvan wrote...

Molten lead *will* char the wood, but probably not enough to matter. That's
what I do to weight my son's Jummywood Derby cars. It works fine. I made
a little crucible out of some scrap copper, with a pointy pouring spout on
one end.

Me too, exactly the same thing. I haven't had a problem with charring,
though, just a little at the edges of the hole (and inside it, of
course). But as long as the thickness of the piece is reasonable, it
doesn't char through.

It flows at a relatively low temperature though, and if you get the amount
of drop just right, it will still be liquid, but will have cooled almost to
the point of being solid again by the time it hits the wood. The trick is
to pour a little, let it cool, pour a little more... If you fill it to the
top in one shot, the lump of lead will stay hot longer, and have more time
to char the wood fibers.

Silvan's technique is more cautious than mine. I complete the pour in one
go, but I do fill the hole at just a trickle, and I pour with the lead
cool enough that it solidifies within a few seconds after the pour is
finished.

BTW, the lump of lead always shrinks a bit, and the wood does, too, owing
to the moisture lost from the heat. It's a good idea to drip in a thin
glue around the lead after it cools to fill the gap.

Jim