BIRCHWOOD CASEY® OFFERS YOU THE BEST WAYS TO TOUCH UP SCRATCHES AND WORN SPOTS OR EVEN COMPLETELY REBLUE MOST GUNS. IT WILL GIVE A NON-STREAKY, EVEN BLUE-BLACK FINISH TO STEEL (EXCEPT STAINLESS). BOTH PERMA BLUE® LIQUID GUN BLUE AND PASTE GUN BLUE PROVIDE GREAT BLUEING TO METAL THAT HAS ALREADY BEEN THOROUGHLY CLEANED AND IS FREE OF RUST. PERMA BLUE® PASTE GUN BLUE IS SLOWER TO DARKEN THAN LIQUID GUN BLUE, BUT WILL BUILD UP A DENSER FINISH. NOTE: PERMA BLUE® LIQUID GUN BLUE WILL NOT BLUE STAINLESS STEEL, ALUMINUM OR NON-FERROUS METALS.