I have anaglyptic embossed wallpaper that I painted with a metallic faux finish to look like patina on copper. You have to prime the paper first with something like Zinsser and let that cure completely. You can use latex or acrylic paint over that, but most metallic colors only come in acrylic formulations and you can find some in larger containers. I used a basecoat over the entire paper first then came back over the high spots with my patina green on a very dry brush. I had a damp rag handy to wipe off immediately paint that went where I didn’t want it to be. Another hint, take a scrap piece of the wallpaper and experiment on it before you hit the wall to get your technique and color blends the way you desire.