How to remove patina from copper ornaments?

Dip the cloth in vinegar, and then wipe it with proper amount of salt or squid bone powder to remove the green rust.

A little more complicated:

We can remove the rust by mechanical friction, but it is not only troublesome, but also damages the surface of bronze ware. Here is a good way to remove the patina. Measure 20 ml of concentrated ammonia water with a measuring cylinder and put it into a beaker, then inject 40 ml of distilled water and stir it with a glass rod to make an ammonia water solution, that is, copper wiping water. Copper washing water can react with copper rust to form soluble blue copper ammonia complex, thus removing copper rust. In order to improve the effect of removing the copper rust in the copper wiping water, chalk powder or talcum powder can be added to the copper wiping water, which can increase the mechanical friction, fully expose the deep copper rust, ensure the complete reaction of the copper rust with ammonia water, and make the bronze surface smooth and bright. Dip cotton in copper rubbing water and scrub it repeatedly on copper products with copper rust. Soon, the rust on the surface of the bronze disappeared, the copper products showed bright metallic luster again, and the cotton was dyed blue. When the patina on some copper products is difficult to remove, it can be soaked in copper wiping water for a while, and then scrubbed with cotton dipped in copper wiping water.