Why are his coins in good shape relative to other emperors?
Lots of hyperinflation in this century, and so many more coins survive just because more were around. Also, the silver content is still high enough that the coins are not as easily corroded by the environment as they will be half a century later.
Did each emperor delegate responsibility for the minting QA so that there are varying qualities between emperors?
The imperial mints were always in charge of coinage, the emperor had little to do with it except perhaps for the motifs used. The silver content staid fairly stable around 95-85% until the 160s CE, after which the denarius was replaced (more or less) with the antoninianus I posted here, technically worth 2 denarii but with only the silver content of one (~40% fineness).
The fineness of the antoninianus also declined, and in 274 AD it was around 5%. Diocletian would replace the antoninianus with his own coin, the follis. It was a large chunky billon coin with a silver wash. He also introduced (in limited number) a true silver coin called an argenteus.
Here’s an illustration of the declining silver content in the antoninianus.
Lots of hyperinflation in this century, and so many more coins survive just because more were around. Also, the silver content is still high enough that the coins are not as easily corroded by the environment as they will be half a century later.
The imperial mints were always in charge of coinage, the emperor had little to do with it except perhaps for the motifs used. The silver content staid fairly stable around 95-85% until the 160s CE, after which the denarius was replaced (more or less) with the antoninianus I posted here, technically worth 2 denarii but with only the silver content of one (~40% fineness).
The fineness of the antoninianus also declined, and in 274 AD it was around 5%. Diocletian would replace the antoninianus with his own coin, the follis. It was a large chunky billon coin with a silver wash. He also introduced (in limited number) a true silver coin called an argenteus.
Here’s an illustration of the declining silver content in the antoninianus.