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Commodus Sestertius: About Authenticity And Other Questions

 
 
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New Member
Germany
29 Posts
 Posted 01/07/2019  9:58 pm Show Profile   Bookmark this topic Add DirtyHarry to your friends list Get a Link to this Message
Good evening dear gentlemen,

I came across this specimen which has lots of surface bumps and looks more copperish than other sestertii I had.
Is it somewhat uncommon or just plain fake? How does one explain these bumps in the minting process? Or are they rather related to later corrosion?

The coin weighs 17.4 grams and is around 26-27 mm. in diameter.
It comes from a well reputed german numismatic house.

I attach some pictures at the end, along with some pics of the edge.

Thanks to everyone in advance for sharing your thoughts and knowledge!
Cheers,






Valued Member
United States
428 Posts
 Posted 01/07/2019  10:12 pm  Show Profile   Bookmark this reply Add jskirwin to your friends list Get a Link to this Reply
Bronzes aren't my specialty but given the bumps appear clustered in areas I'm thinking corrosion. I believe casting bubbles are more uniform. The fields behind the head, on the hair, and in front of the forehead look good. The edges look good.
I would guess that your coin spent 1,700+ years in the ground and shows it.

But again, not my specialty. Check the fake reports here: http://www.forumancientcoins.com/fakes/
Bedrock of the Community
Australia
14959 Posts
 Posted 01/08/2019  12:34 am  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
jskirwin: I would normally think 'casting bubbles', but in this case, I think you are on the right track.

The reason for my support has to do with looking at the edge pictures. Orichalcum (alloy of zinc and copper - a Roman coin alloy of brass), has a paste range for the alloy. The paste range for any alloy is in between the melting points of the lowest and highest melting points of the metals which make up the alloy.

Melting point of zinc 420 deg.C, melting point of copper 1083 deg.C, giving a temperature paste range of 663 Celcius degrees, that is quite a large temperature paste range. If zinc was say, 15% of the alloy, the metal paste would be fairly stiff, but good for relieving die stress.

This produces the cheesy sort of texture of the alloy as seen in the edge pictures. Ancient coin flans were often heated to soften the alloy, so as to extend die life. Dies were hand cut and were expensive to produce.

The edge split has sharp edges which is the result of tensile metal distress, such as what is found on the head of a well used cold chisel.

The sharpness of the hair detail and nose line still suggest to me that this coin was struck, not cast.
Therefore, the textured surface in places has to be the result of corrosion, not casting.
Edited by sel_69l
01/08/2019 06:54 am
Pillar of the Community
Belgium
1142 Posts
 Posted 01/08/2019  06:04 am  Show Profile   Bookmark this reply Add antwerpen2306 to your friends list Get a Link to this Reply
Is the weight correct ? It has to be 10 gr more normally . The size also is a little small , but acceptable .albert
New Member
Germany
29 Posts
 Posted 01/08/2019  8:40 pm  Show Profile   Bookmark this reply Add DirtyHarry to your friends list Get a Link to this Reply
Hi albert! Yes I think so. The coin is definitely lighter and smaller than any sestertii I had in my hands, but I wouldnīt say itīs ten grams lighter than it should.
Trying to educate myself today I found lots of sestertii from the times of Commodus weighing around 20 grams and a few (also authentic) between 20 and even 16 grams.

According to wildwinds, this particular one should be a Sear 5797 / Cohen 645.

Edited by DirtyHarry
01/08/2019 9:59 pm
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