any ideas for cleaning this one?

[ozalan]

Hi, has anybody got any ideas as to the best way to get rid of the green deposit on the obverse of this Theodosius II. It's not very thick but it's quite hard and I don't want to scratch the coin.
There is actually quite a nice quirky portrait underneath the green stuff and I don't want to ruin it!

Many thanks

[casata137ec]

Man...with the lighting it is really hard to tell what's what on your coin. Sorry that no one has replied before this, but really, the green that you are describing sounds like the patina and really shouldnt be messed with too harshly. If at all possible, could you take another set of pics with a bit better lightling?

Chris

[ozalan]

Thanks Chris, It just don't look like "normal" patina to me. The dark brown patina seems to be underneath. The green layer looks like something has been touching the coin and reacted in some way to make it. The green deposit looks almost crystal-like.
 I've attached another pic of the obverse, hope it's better.
It's not the best coin but it's the first Theodosius II I've found in an uncleaned lot.

Many thanks

[Tiberiusjulius]

Perhaps it could be bronze disease?

[ozalan]

Nope, don't think so. The green stuff is too hard and doesn't look right for BD. I've had quite a few coins with BD but this is something else!

[larry c]

Looks like crystalized copper cupric.
Rock hard crystal stuck to the flan over the patina.
Soaking may loosen the weak spots, but mechanical cleaning is
the only way I've found to remove it.
Long DW soaks and slow& easy, preferrably under magnification.

[ozalan]

Thanks eveyone for their thoughts,
I think you must be right Larry, the description seems to fit.
I'll post a pic of it again when I've made headway with getting rid of the copper cupric! A long slow process (as usual)

Many thanks

[larry c]

Here's a quick scan of what looks like the same kind of deposits
before & after. I started in January, long soaks, then light mechanical
then back in the DW soak. Slowly working the deposits down.
Don't try to hurry it, the stuff just gets more stubborn! 

 

[ozalan]

Thanks Larry, you've done a really excellent job on that coin. It gives me hope that with a bit (maybe a lot) of patience the Theo II will clean up nicely.

[casata137ec]

Yeah, good eye Larry! Thanks for the example. And I would also like to echo the good job on the cleaning!

Chris

[larry c]

Thanks guys, with a coin like that I try to hit the most encrusted spots lightly then set it aside in DW and work on something else for awhile.
Sooner or later, usually later you run out of spots to clean!
I limit the time I spend on it, when you push on the green rock the easier
it is to scar the coin.

with a bit (more likely a lot) of patience the Theo II will clean up nicely.