I think your descriptions and titles are pretty good, actually. The only thing I'd say is change the order of some words.
"Chain-maille silver-plated bracelet" ----> "Chain-maille bracelet silver plated" As in the first sentence of your description, you refer to this piece as a Chain-maille bracelet. That's what people will search for first and colour or metail is a secondary filter. Therefore, my title would keep those words together and toss in the secondary filter words after. Also, as a tag for this item, I would include "chain mail" or "chainmail" because not all people will know the correct spelling.
"Onyx, crystal and gold floating necklace" ------> "Floating Necklace Onxy, Crystal and Gold"
Just my thoughts.