Finished soaking, neutralized the acid with baking soda and water and sprayed on some WD-40 - the teeth seem sharper, just as with files.
Don't know if the Vini-iron concoction will give the rusty-brown I'm looking for on wood, but it sure stained my hand rust-colored, thanks to a hole in my glove.
It was posted here before, but the link din't show up in the post - I came across this video on hand cut rasps that others may enjoy
And this vid for hand cut files