"Tom Storey" wrote in message
news:Lj4nf.95140$Gd6.22530@pd7tw3no...
Is it just my imagination or is my 'Kingspore' brand waterproof sand paper
leaving black marks on some of my work? Ok, I know you can't see it!
However, I've been working with white birch and it sure looks like it's
darker in spots after I've sanded it, both dry and with a blo/thinner mix.

How does the 'dark red aluminium oxide' waterproof paper perform and will
it leave a stain?

Silicon Carbide (SiC) grit doesn't fracture like aluminum oxide, which is
why it abrades as full grit from the glue into the raw wood sometimes Plus,
it's normally mounted on thin paper, where creasing and flexing knock off
even more. That's why I don't use it on raw wood. Once you have some finish
between the paper and the pores it's easier to wash off the mix of cellulose
and grit with a bit of solvent.

You can use the Klingspor gold cloth-backed stuff wet, so I'm told. I've
never given it more than a few brief tries, but it seemed to hold and not
color. Haven't encountered any red wet/dry, but if it had a more flexible
backing, it would seem a better choice. Aluminum oxide is almost colorless
in the mineral.