Help cleaning this nice Constantius II AE2 from Rome.

[seth]

Hello everyone.

It's been a while since I last posted here. Here is a scarce coin I got in a Spanish lot:

AE2 23mm 6.3g Constantius II Centenionalis/Maiorina 350AD.
OBV: DN CONSTAN - TIVS PF AVG; laureate, rosette diademed cuirassed bust right holding globe in right hand. A behind bust (?)
REV: GLORIA ROMANORVM; Emperor on horseback spearing barbarian with Phrygian helmet, shield and broken spear under the horse. * in right field.
EXE: R B
REF: RIC VIII Rome 205, R3

As you can see, the reverse is quite nice, the problem is with the green encrustations on the obverse. Is there any way those encrustations could be removed without losing the patina?
Thank you.

[BiancasDad]

Seth,

I would leave it as is. I have never had any success in trying to improve a coin with these type of deposits. I am not saying it can't be done, but I think the risks far outweigh the rewards. It looks like the patina would certainly be at risk and it doesn't look like the details on the obverse are as pronounced as the reverse anyways. I think trying to remove the deposits would more likely give this coin an unnatural look and possibly make an ugly mess.

As it stands, the coin has a nice character to it and a lovely reverse for this type.

Cheers, -Kurt

[seth]

Hello Kurt

Thanks for your advice.

[seth]

New, better pic:

[SC]

Seth,

I have had those hard green deposits (malachite) come off nicely with a sharp scalpel.  BUT only when the surface underneath, and for that matter next to, the encrustations is smooth and even and stable. 

In my experience this occurs on two patina types. 

One is where the surface is otherwise a smooth rich-brown toned bronze.  I have this on many 2nd century AD sestertii and on some 3rd and 4th century coins (Gallienus Ants and Constantinian bronze).  In all these cases the surface is very nice other than the encrustations.

The second type is on silvered coins, either the XXI type Aureliani of the 270s-80s, or coins of the 310s - 320s.  Again these all have a nice smooth silvered surface other than the spots that are encrusted.

In all these cases the malachite can pop-off when I use a scalpel under magnification.

I just can't tell from the photo of yours what quality the rest of the patina is.  Is does not look completely even and smooth.  If that is the case then you risk what Kurt noted - the chance of leaving an ugly mess.  You might want to try removing a VERY small bit of the encrustation with a scalpel to see what happens.  But only if you feel comfortable.  It is a very nice coin.

Shawn

[seth]

Thank you for your suggestion, Shawn.
I think I shall try the scalpel/needle pin method you pointed out, will return w/ notes on progress for anyone who might be interested.

[Caesarea]

 This is a hoard coin, fact.
The green lumpy deposits are where coins together leach their oxides onto each other. generally the coin surface underneath is superb and there are methods which work, and which will not damage the patina either.  I cannot share them here as they are dangerous and that would be irresponsible.  There are no chemicals involved, but as I say, dangerous.
The red bits on the reverse suggest a certain amount of BD so expect pitting there.