if it is a metal yoyo u can get a metal tin and put gobs of jasco stripper or similar, or sometimes u find paint and varnish stripper in spray cans spray it on itll be like snot then close the lid come back in 10 min then hose it off away from anything made of plastic or paint or other stuff the stripper will turn into snot, and like mentioned by someone else wear gloves, water will neautralize the stripper it is a acid…
avoid using oven cleaner it WILL remove anodization
i had to do the same thing to a metal yoyo i was experimenting with stuff to use in the response groove, Plumbers goop works real good for me, and it dries like a rubber band.
i also use a dremel with adjustable speed and a plastic wire brush to remove any exess