I recently found some old sharpening stones in a garage sale. They were covered in oil and looked horrible and everyone passed them by. I paid $3 for six stones. When I arrived home, I took a spray can of brake cleaner and sprayed them well. After a few minutes, I washed them off with a garden hose. They came out like new, all the oil and buildup metal in the stones was gone. The metal filings came out of the pores with the oil.