Place copper blocks, cut copper, copper stairs, or copper slabs in the open air
Wait for them to oxidize naturally over time
Do not use a honeycomb on them if you want oxidation to continue
Use a lightning rod nearby only if you want to prevent lightning damage, not oxidation
To speed up oxidation, place more copper blocks close together
To stop oxidation at a specific stage, use a honeycomb on the copper
To reverse oxidation, use an axe on the copper
To fully oxidize copper faster, keep it exposed and leave it unchanged