The trouble with lacquers is two fold:

Firstly they destroy the natural lustre of metals and what you get is a kind of shiny plastic glaze.
Secondly, they inevitably chip and wear unevenly, leading to patchy tarnishing eventually.
As a result, many jewellers use a micro crystalline wax such as Renaissance Wax, or any other high quality wax polish, which gives a more professional result.

If you still wish to go the varnish route you might consider a tough spray on, such as clear polyurethane, or cellulose as used on cars. They all have different degrees of shine and texture when dry. They are also toxic to breathe and are best used wearing a mask and if possible out of doors or with good ventilation. Dennis