At the urging of Cindy Eid, I am posting the results of my off-line
discussion on this topic with her. It appears that my using a brass
brush, without the use of soapy water, and bearing down on the brush
in some places, caused the brass to transfer onto the AS pendant.
This is probably why I saw the tarnish in "spots" as opposed to an
overall tarnish. I also did not finish the piece with Goddard's,
which Cindy advises is available in liquid and cloth forms. I will be
placing an order today!
Thanks again to all who contribute to the body of knowledge known as
Orchid, and thanks, too, to Cindy for her kind and thoughtful
answers to my questions.