A Chemistry Experiment
This coin interested me for several reasons :
the link to the time when the Roman senate declared war with Jugurtha
the portrait of Mars on the obverse - the facial features are less exaggerated than other dies in this series
the tripod control on the obverse
the eagle between RO and MA on the reverse
the metal on the right edge, which invites a chemistry experiment
The moneyer was a member of the gens Cornelia, one of the most illustrious noble families in the republic with many members holding political and military leadership roles. Servius Cornelius Cossus Maluginensis was first member of this family to hold the consulship, early in the history of the republic in 485 BC. The republic began in 509 BC when king Tarquinius Superbus, was overthrown by Roman nobles led by Lucius Junius Brutus. The name Blasio derives from "blaesus" which refers to a lisp or stutter. This branch of the family going back at least as far as Gnaeus Cornelius P. f. Cn. n. Blasio (son of Publius and grandson of Gnaius born of Blasio), consul in 270 and 257 BC. Reviewing the Richard Schaefer die study, I didn't find a die match for my coin. I was curious to see if I could confirm the expected reverse control and find evidence that the coin matched an official die. While no match - I did find that the style is very consistent, and the control that is paired with the tripod is always the dolphin (although I cannot convince myself that a dolphin is visible on my coin).
This coin was issued in 112-111 BC, as the republic had declared war on Numidian king Jugurtha. This war would result in a career boost for Sulla as the one who captured Jugurtha and it would fuel the bitter rivalry between Marius and Sulla.
And indeed Sulla himself was naturally vainglorious, and now that he had for the first time emerged from his lowly and obscure condition and become of some account among his countrymen, and was enjoying a taste of honour, he was arrogant enough to have a representation of his exploit engraved on a seal-ring which he wore, and continued to use it ever after. The device was, Bocchus delivering, and Sulla receiving, Jugurtha. - Plutarch, The Life of Sulla, 3.4
I decided that I was willing to risk damaging this coin in the interest of an experiment, the key questions that I wanted to explore: can I improve the way the coin looks with a little cleaning and is this a fourrée?
The starting point:
Cn. Blasio Cn.f., 112-111 BC, AR Denarius, (18.2mm, 3.85g, 6h), Rome mint Obv: CN BLASIO CNF, Helmeted head of Mars right; tripod to left, mark of value above (off flan) Rev: Jupiter holding a sceptre in right hand and thunderbolt in left hand, standing slightly left between Juno and Minerva, Juno holds a scepter in her right hand and Minerva is crowning Jupiter with a wreath and holding a scepter in her other hand; there is a palm frond between Jupiter and Minerva, [an uncertain control letter/symbol - most likely a dolphin] to outer right; in exergue, an eagle between RO MA. Ref: Crawford 296/1i; Sydenham 561e; Cornelia 20; RBW – Notes: Toned with some deposits in the devices and some metal flaws.
The reverse control on the right side is most likely this dolphin:
a close look at Jupiter's legs shows the roughness of the metal on the reverse:
Crawford (RRC 1974) rejects the theory that this is Scipio Africanus on the obverse, and argues that the peculiarities of this obverse portrait show up in other contemporary coins e.g. this Roma with long narrow neck and exaggerated features: cheek bones, nose and chin.
Step 1: soaking a little sodium thiosulfate pentahydrate, dissolved in warm water...
Zooming in on Jupiter's legs the grainy surface is much improved.
Step 2: a little vinegar mixed with water and gently brushing with a soft toothbrush...
this brightened the coin a little, but otherwise doesn't seem to have done much. Looking at the right edge, I was beginning to be convinced that this is a fourrée.
Step 3: I decided to try another round of sodium thiosulfate solution - this time I tried warming the solution gently on the stove...
Overall this darkened the coin a little more and a noticeable grey dust could be seen in the solution, and it took the dark edge off of the right side to reveal good silver underneath! so NOT a fourrée is the conclusion. Another look a Jupiter's legs shows a good surface and dark toning not in my view over-cleaned. Although it doesn't show up in the photo - I can see a better outline of the dolphin control on the reverse as well in the cleaned coin - a raised curve blending with the edge of the coin.
While I could go further and remove the remaining silver oxides from the right side of the reverse, I am happy with the coin as it is and no longer willing to experiment. The final coin weight is 3.78g - a change of 0.07 which can be explained with the oxides and other debris that were removed. From my perspective the coin in hand is overall improved.
"Horn silver" or silver chloride (AgCL) is one of the silver salts that is found on ancient coins. In a hoard of coins, as some of the coins degrade they deposit silver chloride on other coins which adheres to the surface. This explains why the coin underneath is not damaged as I remove the horn silver. I think (I am not certain) that this is at least a component of what was removed from this coin with this reaction: AgCl + 2Na2S2O3 → Na3[Ag(S2O3)2] + NaCl.
Would I try this again? Yes - but with the same caveat that I mentioned at the start - I would only attempt this with a coin that I would be OK damaging.
References (in addition to others directly linked above)
Crawford, Roman Republican Coinage, 1974, Cambridge University Press
Figures de l'histoire de la République romaine, accompagnées d'un précis historique : ouvrage exécuté par ordre du gouvernement pour servir à l'instruction publique, Mirys, Silvestre David, et al. 1799, Paris, Chez le citoyen Mirys