Claudette, I have to ask, what is black enamel stick?
I have googled black enamel stick, and can not find any reference to a black enamel stick in jewelry making. I did find some information on black enameling which is a finished applied by using colored glass powder and heating it to melt on the piece of metal. This is a difficult process, and not everyone should attempt without first taking classes.
Oooops, sorry. Should have had comma after that enamel, and before stick!
Once a jeweler friend of mine told me, I actually tried it and it's easy and does work great and it's fairly permanent.
Take glossy black or flat enamel, depending on what kind of look you want - you can go to the hobby store and buy a bottle of model paint. Using a small artist's paint brush, fill in the nooks and crannies, then wipe off with a soft, clean rag. The rag will not get into the nooks and crannies, only the raised parts. If you get too much, an acetone based fingernail polish remover will remove it, using either a clean paint brush or rag. If you want some parts darker, just apply more paint with the tip of your brush, taking off the excess with the rag.
If you get tired of the "look" remove with acetone and a toothbrush.
If it is a ring that you are wearing every day, of all of the oxidation processes this is the one that will last the longest, but not forever, It just wears off after years of washing your hands, etc., then you just do it again.
Good luck. Sorry about my punctuation error - I either use too many or not enough!
Tip: To stop metal findings from tarnishing store in a ZIP Lock bag with a chunk of chalk.