Cleaning and Stain Removal - Help please stained quarry tiles

I have unearthered an original red quarry tiled floor, but when i pulled up the laminate flooring, it revealed what i now believe to be dried urine on the tiles, the smell was totally yuk, the room was used by the previous owners as indoor kennels so i assume it was dog urine, it has left a black dried stain, it is in almost ripples where it had soaked under the liner. I have tried paint stripper, sugar soap, bleach, washing powder, what else casn anyone suggest.. the smell has gone but i cannot get them clean, so please please can anyone help,, thanks for any tips at all, btw is it possible to do something to some of the tiles which are slightly pitted, a sort of re-dressing of the top surface if this is possible..thanks

quarry tiles are not meant to be finished or "waxed" so i dont think you can redress them...an acidic cleaner may help remove the spots....but i think whoever overliad the floor did it for the same reason