Seal with several coats of polyurethane. Marine grade varnish. Bullseye Sealcoat shellac. Automotive clearcoat lacquer
Geo: maybe a product like this would help
William has the answer. Seal it at the point you like the color. If inside use polyeureathane if out side Marine Varnish. Enjoy, I love copper.
You must lacquer the copper to prevent oxidation............
Hi Goe: Coat the copper item in a protective coating to prevent future discoloration. Coat the item in beeswax or carnauba wax. Dip the soft cloth in the wax and apply it to the copper surface. Buff with a clean soft cloth. Here's a site that should help:
Apply a clear sealer to the copper so the copper doesn't oxidize by being in the elements.
Hi Geo, A day or two after the patina process, when the patina is finished and dry, seal it using a clear spray lacquer. Apply at least three light coats of lacquer on every patina surface of the metal, drying each coat thoroughly before applying the next coat. Hope this helps you
Hi! A clear sealer will keep it looking the way you want. You may have to repeat the sealer at a later date. Good luck and stay safe!
Here's a post that might help you - https://www.hunker.com/13416142/how-to-inhibit-or-stop-the-copper-patina-process
I'd use a sealant!
Try spraying a varnish or a scotch gard over it
Add a clear sealant. Probably a spray on version would be best.