Unlike modern mints, where you have 24/7 CCTV surveillance at every corners or the metal detectors that the workers have to go through, in the olden days do you think some workers would just 'pocket' some of their work on their way home? I know that some of them were corrupt, for instance during the reign of Aurelian, although that was systemic. What sort of supervision would've been there? It's not unreasonable to think they'd just swallow a couple of silver/gold coins and retrieve them the next day (much easier with those tiny Greek fractionals).
I thought I read they were issues X pounds of metal and were expected to return X coins. That is how they controlled for that. For precious metal coins, weight per coin was also evaluated, but for coppers they didn't care as much which is why we see more deviations in weights. Interesting point though. I wonder if some weight variations were driven by theft, mint employees stealing half a gram per tetradrachm for example.
It probably did happen, though likely not on a wide scale. Given that slaves often worked in the mints, I imagine the punishment for theft of materials and/or coins would have been quite harsh.
some moonlighted and made their own money-- Theodosian Code 9:21:2 Since some imperial minters are secretly and criminally engaged in the coinage of counterfeit money, all shall know that the necessity is incumbent on them of seeking out such men, that they may be tracked down and delivered to the courts, so that they may forthwith betray the accomplices of their deeds through torture and thereupon be sentenced to suitable punishments. (20 November 321) and some stole silver from the mint-- 9:21:6 We have learned that some metal casters purge the majorina criminally and frequently, by separating the silver from the bronze. If any person hereafter should be apprehended in this trickery, he shall know that he has committed a capital crime. Also those persons who furnish the use of houses and lands to counterfeiters must be punished by the delivery of their property to the imperial largesses. Of course, Our Clemency must be informed of the names of such persons. (12 Feb 349)
Yeah, you don't mess with the sacred money goddess: Constantius I Caesar, A.D. 293-305 Augustus, A.D. 305-306 Bronze Nummus Siscia mint, A.D. 300-301 Obv: CONSTANTIUS NOB CAES Rev: SACRA MONETA AVGG ET CAESS NOSTR - Moneta, standing left, holding scales and cornucopiae SIS in exergue; ✳ in left field, B in right RIC 135a 28mm, 9.5g.