Protecting plating from tarnishing is the bane of many designer’s existence! Sometimes you simply cannot replate a piece because it’s been set with pearls or porous stones. This is why each gold plated sterling piece in the Amoracast brand is protectively coated with a high-temperature baking process. Although we love precious metals and try to deal only with them, sometimes using copper is necessary. It is a conductive material that can be painted on so if the stone is rugged, instead of using sterling strips that are difficult to wrap every bump closely, the copper can be applied closely and then it will plate gold or silver nicely. So, you will see copper used even with fine, rugged or bumpy stones. With time comes the patina, and if you don’t like that, just lacquer protect the pieces.
You can protect plating from tarnishing by using jewellery lacquer. It is available at silversmithing supply stores, and smells like wood varnish, but with a lighter consistency. You can brush it on and hang dry it or dry it on a steel bristle brush (dries in a couple hours). You don’t need a lot and it’s effective for a long time. Acetone, which can be bought from jewelry supply places; or can be found in cheap nail polish remover, is good for removing mistakes and excess lacquer. Also good for removing excess lacquer are light wood chips and non-fuzz paper towels, just make sure to do this in a well-ventilated area!
Here’s a Youtube video demonstrating how easily it can be done!