Verdigris, what some people refer to as green “gunk” on Chinese antique bronze, is a natural form of patina that accumulates over time on copper, bronze and brass as it is exposed to air. In addition to varying shades of green, it may also be bluish green in color. It can also be induced using acids, and sometimes is artificially applied to new items made of these metals, especially copper.
Does Verdigris Damage Chinese Antique Bronze?
Verdigris would not be considered damage if a natural amount of verdigris is present. Since this is considered to be patina, it actually preserves the value of rare pieces to leave them as is.
Should You Clean Verdigris?
Since verdigris on Chinese genuine antique bronze objects is viewed as patina and thus adding value depending on the rarity of the piece, it’s best to thoroughly research the impact cleaning will have on each type of metal antique or collectible before tackling those projects, personally I would NEVER clean ANY Chinese bronze items, but if you must then it is imperative you consult with an expert first.