Do you have to sand the furniture piece before using metallic paints?

Any paint needs something to adhere to when used. I would lightly sand the furniture to remove the shine, wipe it with tack cloth then use a primer before using the metallic paint. However, look at the directions on the paint itself. It should tell you how to use it on a shiny surface, although if it's more of a craft paint, it might not have any instructions for furniture. In that case sand, wipe, prime & paint. :) Wishing you the best & Happy Holidays.

http://thegraphicsfairy.com/use-metallic-gel-stains-furniture/

https://www.hometalk.com/b/915980/diy-paint-transformations

No, on just painting over existing finish, the metallic will streak and not cover well. Best to at least use Liquid Sandpaper over the piece to give the surface "tooth" so the paint will adhere well.

Good prep will give you a better outcome.

Thank you!