I used to get black crackle finishes to look real new while I was in the navy
in the fifties. I used flat black enamel paint and thinned it so it would
flow about like the thinner flowed with no paint. Basically I just floated the
stuff on and wiped immediately over it with a cloth to take the black off the
lettering. Sometimes took two treatments but it always worked very well.
(broke=not working, retired=not working, retired=broke)