At the end of last year we collected a pile of surplus stones from Manchester Metropolitan University Printmaking Department. They've been used for many years as ink slabs and are pretty nasty to look at, as well as pick up.
A careful chisel helps remove the ink build up on the edges before being leveled and resurfaced. The stone storage situation will have to be looked at again to find homes for them.
Thanks to Nigel Easter & Paul Hughes for being helping hand white van men and Howard Goody at MMU.