Green Copper Corrosion - Chemistry

Couple of links to help out some-
http://www.dirtyoldcoins.com/shop/s...s/index.html
http://www.coinworld.com/news/062507/BW_0625.asp

Thad, I'm a little shocked at the statement of Verdigris. As a chemist you must be aware that Verdigris is Copper Acetate and not the usualy Green discoloration on Copper coins. Everyone should be told that not all green discolorations on Copper coins or anything containing Copper is usually NOT VERDIGRIS. Again, Verdigris is created by the exposure of Copper, Brass or Bronze (All are made of Copper) to an Acetate. Other greenish patinas on coins are usually Copper Oxide, Copper Carbonate, Copper Sulfide or Sulfate. Each type of such compounds may be dissolved or removed differently from the original coin or object by numerous different methods. Such discolorations are common on Copper tubing, grounding wires, other Copper products. The Copper Sulfites and Sulfates are highly soluable in distilled water for example. Copper Carbonates are usually not quite so soluable and the removal will naturally remove some of the original coins material.
The primary problems with items like Witch Hazel, Olive Oils, Peach,Tomato, Orange or Lemon Juices to remove such contaminations are the in the inconsistancies of those substances. Practically all such substances are run through a manufacturing process where the end results could be and usually is slightly different from one product by one manufacturer to another. This means that what may have worked for one person may be a dissater for someone else. Only a natural element is consistant. Man made products consistantly change and usually do due to proprietary product processes.

Carl - Perhaps your definition of verdigris is a matter of semantics. If you read on the subject, basically any chemically reacted material present on yellow metals can generally be called verdigris. Example:

http://en.wikipedia.org/wiki/Copper_carbonate




Nonetheless, my approach reacts with sulfate, carbonate and acetate anions. I don't much care of the exact verdigris chemical composition at this point, other than they are copper complexes. My trick is forming those free anions and preferentially reacting them so they go into (and stay) in solution.

What a relief! My collection is safe from copper-eating microbes!

If you wanted to bury old gold coins would dipping them in olive oil, sealing the bag, then wrapping them in a 3mil trash bag before dropping 3 feet in a hole- would that be ok?

crhsb: I too like to read those type of items. However, be carefull of what some say. Remember there are people out there that just blab with no experience, just a lot of guess work. Note, for instance, the one link is specifically for the sale of a product it appears. If it doesn't work, OH well, to bad.
I like this one about the Olive Oil.

Olive oil not just for cooking
Hobbyists use 'fruit juice' to remove verdigris
posted 6/12/07
By Paul Gilkes
Coin World Staff
Olive oil has been used as a softening agent for ages to aid the removal of built-up verdigris or dirt accumulations on coins that are up to centuries old.
Some collectors swear by it. Other collectors, and some conservators, swear at it, claiming the fatty acids that the olive oil contains can actually damage coins, particularly copper.
Ironically, copper or copper alloy coins are usually the subject of the olive oil immersion process.
However, in all fairness to Olive Oil they mention the pro's and con's both. The problem with stories like this is they always forget to mention that not all products such as Olive Oils are the same. Any product made in a manufacturing organization has a proprietary process for patent infringement purposes. Such methods could and usually do make things different so that an Olive Oil I use is usually different than one you may buy. May or may not have an adverse effect.

jbuck - LOL!