You will need:
6" x 6" prepared canvases (available at any art supply store)
Sheet copper -- 24 or 26 gauge (you can buy pieces at BeadFX and cut them down)
Plumbers solder (pick up at a hardware store, comes in a spool about $25)
Flux (you can use Handy Flux or pick up flux at the hardware store sold alongside the solder)
Torch (any torch from a small one to a propane or MAP gas torch will work)
Cross locking tweezers
Rawhide or nylon hammer
Alcohol ( not that kind! Isopropyl alcohol)
Glue (I like E6000)
Prepare a working surface and paint the canvas. If you want an uneven surface, first put down modelling medium following the instructions on the jar. Let dry then paint.
Cut out your copper squares (or rounds or any shape you're inspired by!) and file any sharp edges and slightly round the corners. Flatten gently on a bench block. Clean the copper of surface dirt and oil using steel wool and isopropyl alcohol. On my examples, each square is 2" x 2".
Place the copper on a solder block and paint with flux. Cut several half inch pieces of plumbers solder and place them on the fluxed copper square. Heat the solder directly with your torch until it flows. Turn off your torch and press your chosen stamp into the solder. The solder will take the imprint of the stamp and excess will blob out around the stamp, if you used a lot like I did. If you use less solder you will get tidier results. Experiment with it! Remove with tweezers after it cools a bit and quench in some water.
If you want, add a few drops of alcohol ink and blot to mottle it or create different effects. Then glue to the canvas. On the single square example above, I glued the copper onto the painted modelling medium then covered the whole piece with several light coats of resin, which you can purchase at art supply stores. Most canvases will come with finishing hardware. If not, you can pick that up at a hardware store too.
Enjoy this technique. Photo idea bonus, for those who aren't comfortable with metal and torches. For this birch canvas hanging on the small wall inside my front door: I painted it with black gesso in a swirl pattern and then glued down a vintage button I embroidered around with Czech fire polish beads,vintage silver three-cuts and matte black delicas. Easy and very pretty.