We can recommend the following repair service:

BEST JEWELRY CONTRACTING
RON TENEBAUM
Please contact him directly:
212-398-0490

If you prefer to have you local jeweler repair your piece,
click on the jeweler’s repair instructions below for some helpful information.

General Instructions for repairing Lisa Jenks Limited (LJL) jewelry:

Many repairs can be done by your local jeweler. The main difference with the LJL jewelry finish is the oxidation (black area) and the low luster finish. Your local jeweler can re-oxidize the silver jewelry using a silver oxidizer.

(You can find one type here)
http://www.rjsintl.com/productDetails.asp?product_id=O10

The oxidizer is applied to the surface of the piece and then polished off the raised surfaces, keeping the black finish in the recessed areas.

To achieve the low luster finish, we used a 3M Polishing Wheel on a polishing motor, low speed.

(you can find the wheel here)
http://www.rjsintl.com/productDetails.asp?product_id=W617-11