Does combining yew with copper or bronze cause any particular reaction, like tannic acid timber would react, I would like to know this before testing it.
I am not sure about the copper or bronze but i think it would need sealing when finished to stop it turning green unless that is the effect you want. You can use fine metal powders and set with superglue or resin. I can post a link to something I filled with aluminum powder if allowed ?
Iron can have an effect and give shades of purple, iv seen this around nails or wire but that's wood grown around it.