All, We used a procedure to blacken sterling that lasted longer than
any other procedure I have ever used. It was as follows:
Complete all soldering and grinding.
Place the piece in battery acid until all the gunk is removed.
The piece should come out of the acid looking matte white. Rinse in
Polish the piece to finish polish. Clean the piece with ammonia
Heat the piece on a hot plate to 200 degrees F. Heat a solution
of liver of sulfur and water to 200 degrees F. We used about two
cups of water to two 1/2 inch chunks of liver of sulfur.
Pick up the piece with tweezers and drop it into the hot liver
of sulfur. Leave the piece in the sulfur for at least 10 minutes.
Remove the piece and wash it in water. Dry the piece.
Prepolish the piece again on a cotton buff, not polishing away
the areas you want to stay darkened. Set your stones.
Finish polish the piece on a clean cotton buff. Clean the piece
with ammonia and water.
This seems like a lot of work, but I have pieces that are worn most
everyday for the last 20 years that are still black.