Quintillus unusual

[Numerianus]

I just purchased this coin of Quintillus.

Quintillus ... (?) antoninianus, Milan mint, 270 A.D.
Obverse: IMP QVINTILLVS AVG, draped and cuirassed bust right, from behind.
Reverse: MARTI PACI, Mars standing left holding olive branch in right and transverse spear in left, P in exergue.
RIC V 58.

It seems that this coin is made from a low grade silver which is very unusual for Quintillus.

[mix_val]

It seems that this coin is made from a low grade silver which is very unusual for Quintillus.

 
If silver it would be exceptional.  Be interesting to perform a chemical analysis (non-evasive like XPS).  How much does the coin weigh?  Celator had an article recently about determining the density of silver coins
 

[Rich Beale]

Although unusual, it would not be unprecedented or suspicious if it were silver. I recently came across an antoninianus of Victorinus struck in good silver.

[curtislclay]

I can't agree: despite its convincing appearance in the image, the fact that the coin is silver makes it very suspicious in my eyes!

As far as I am aware, the many and often gigantic hoards of mid-third-cent. antoniniani that have come to light and been published over the past 150 years have yet to produce a single silver specimen, nor are there any silver specimens in the great museum collections, Vienna, BM, Paris, and so on.

Now genuine novelties do of course turn up, but those facts are enough to make me highly suspicious of an alleged silver specimen that turns up on the market or in a private collection.

It's almost as though a middle bronze of say Nero should turn up, apparently struck in gold or silver: who could believe it?

[Numerianus]

I purchased  the coin from a local dealer. It seems that it comes from an old collection.
To be honest, I was rather suspicious about it. The workout of the hair  (circles and not  dots) and the whole style seem to be a bit unusual. Letters are soft.
I cannot give you a guaranty that the is of a solid metal and not a plated one. The metal looks as a low grade silver or a white-color billon.  The fabric looks ancient. I could  find examples with similar hair engraving for Mediolanum
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The type is common though on CNG there was a heavy specimen claimed to be unrecorded.
  
I show below an example of plated Quintillus antoninianus which is also a unique specimen I ever saw.  To my mind, it is plated rather than silver washed.

[Robert_Brenchley]

Do you have a reference for that one, Numerianus? I have the same coin, but couldn't find it in RIC. Not that that means much.

[Numerianus]

RIC 26, Rome. Here is a copper specimen.

[Arminius]

A couple of years ago i successfully applied very thin tin layers on copper repros of german talers by some reductive process of tin salts in water.
I tried to make them look authetic and ancient (one of these first chemical experiments of a schoolboy).

The surfaces of my "optically improved" taler repros looked exactly like the surfaces of these "low grade silver" antoniniani.

rgds.