i have a ruger service six, the bottom of the trigger guard is nearly bare of bluing. i degreased cleaned, heated and degreased again. heated the guard and have tried oxpho blue, g96 cream, birchwood casey. none will stay at all, the birchwood pen hold better than the others but won't darken hardly at all. the g96 will blacken the guard real good but when i rinse with water it comes off same with oxpho. what doesn't come off in the water comes off when i oil it. the pen leave's a very minor dull finish but nothing seems to be working. i called birchwood casey and g96, they said it may be because the trigger guard was a casting or because since it is a casting the metal inside isn't the same through the whole guard. i'm stumped, can anyone help? i don't need it to match, just cover the bare metal. i thought cera coat but no one near me can blast it so it will stick good. i don't mind bluing wear if it isn't large spots but the bottom of the guard is almost all gone of bluing and i just would like it dulled enough to protect it and stop the shine. thanks for any help.