You would be better to use conventional rhosium plating systems,
which is a beaker of solution, a platinum anode and dunking the whole
ring and plating it. The pen is made for make shift areas, hard to
get areas, not whole rings.
Don't be cheap, buy a pint and the anode, you proabably have the
The ring must be clean and not touched by human hands to be plated.
Does best if electrocleaned first (another $40 of solutions).
Don't plate silver, it will ruin the rodium.