What can I do to clean verdigris?

[gxseries]

I tried to clean verdigris off several copper coins by acetone, but geez, I should have know that there would be almost no effect except against "plastic" and "PVC" damage.

 

Any ideas what to do next? I tried to remove as much as possible with my naked eye and several toothpicks... :/

[Emperor Oli]

I tried to clean verdigris off several copper coins by acetone, but geez, I should have know that there would be almost no effect except against "plastic" and "PVC" damage.

 

Any ideas what to do next? I tried to remove as much as possible with my naked eye and several toothpicks... :/

I don't think it can be removed because it is a reaction with the copper itself, and not just a slimy coating. It can be slowed or even stopped, however, if the air around it has the moisture removed, either by silica gel or a dehumidifier.

 

Also, as I'm sure you know, don't put the verdigris-ed coins with any unaffected ones, as it will spread.

[jlueke]

As the emporer says verdigris ( I am assuming you mean the green crusty rust like stuff) is a chemical reaction with the metal itself. Unfortunately copper alloys are quite suceptible and much touger to clean. If it's on an ancient coin you'd probably try to get the sport off via a solven + pick (tooth or brass). YOu'd still leave behind a shiny spot where the metal hadn't reacted.

[ageka]

copper coins when attacked by chlorides get a selfsustaining reaction

 

(Oddy and Hughes 1970:188):

4CuCl + 4H2O + O2 gets CuCl2 + 3Cu(OH)2 + 2HCl

 

So you need air, moisture and cloride from somewhere

this generates free acid HCl that again will attack the copper etc

 

2Cu + 2HCl gives 2CuCl + H 2

 

 

There are three basic methods

Use the torn of a rosebush to scrape away as much of the green stuff as you can

 

1) put in a soap mixture in a selfheating set like the glass coffeepot on the hot plate leave hot for a day ( keep an eye on the level because you do not want all the water to evaporate and bake the coin in soap )

2) same but use baking soda ( sodiumbicarbonate )

3) if above fails put in 10% ammonia mixture COLD ( dangerous burns your hands etc)

 

In general the rot can be stopped but the mechanical and chemical treatment will allways show

Above methods neutralise the acid that was continuing the rot

[GDJMSP]

I tried to clean verdigris off several copper coins by acetone, but geez, I should have know that there would be almost no effect except against "plastic" and "PVC" damage.

 

Any ideas what to do next? I tried to remove as much as possible with my naked eye and several toothpicks... :/

 

 

A product known as biox will remove it - Click Here

[Ætheling]

You know Ageka i'm sure there's carbonate involved in verdigris as well. I've seen various internet sources stating it was copper chloride, others stating it was a complex hydrated copper carbonate compound. Either way it seems that there is more than one formula for verdigris depending upon the prevailing conditions around when it formed and what shade of green or blue it is.

 

I always figured it was caused by CO2 in the air combining with water vapour in the air making it slightly acidic, and then reacting with the copper.

[ageka]

I read somewhere that the term verdigris is totally wrong if used for bronze rot

 

Anyway the reason that there are a dozen different remedies demonstrates there are probably a dozen different problems

 

I recently had a King Charles X 40 FF with green copperrot in the ear

It toke 3 days in acetone to dissolve the green rot

but that was a 90 % gold coin

 

[Ætheling]

I've seen verdigris on high purity silver coins and i've also seen gold coins with verdigris listed on dealers lists that came in the post. So it's not 'unusual' to come across gold coin with verdigris. Just uncommon.

[28Plain]

Household ammonia is safe to use on verdigris but only on gold coins. It will leave behind a pattern of staining on bronze coins. Ammonia seems to be copper preferential in its attack and will cut the green stuff pretty well but you can always see where it was on a bronze or silver coin. On gold it leaves little evidence that anything was ever there.

 

Don't use ammonia on a CN coin, though. It makes a dingy, porous surface that can only be cleared up by polishing.

[gxseries]

Ah thanks!

 

You see, I wouldn't be in such a fuss if it weren't for these two copper coins that have been bugging me to preserve them or they will threaten to ruin themselves

 

 

Yes, I know, poor quality pictures, but you can see the verdigris and the brown-redness... :/ Maybe I should send them for slabbing but I don't know if they will change over time in slabs...

[Ætheling]

They'd probably turn further in the slabs anyhow.

 

My general approach is to scrape it off. The coin seems to have a bit of lustre anyhow so it shouldn't look as bad. Copper coins are very problematic ones, this is the main reason i avoid them.

 

They lose their lustre easily, the can develop verdigris too readily because copper is rather reactive. In shortcopper is a rather unsuitable metal to make coins out of in the long term from a collector's point of view. They're damned hard to conserve correctly for future generations, silver tends to look after itself somewhat better, gold is the lazy man's metal, gold is as gold does.