Perhaps I should not offer a comment since my study of the matter has not progressed since the page quoted was written but I see on other possible explanation for the clashes being reverses more than obverses. I am not sure I would rule out the dies being made of different materials but, at least, they were made in different manners since the
obverse or anvil die was massive compared to the
reverse punches. Heat treating, whether intentional as
part of the manufacture or accidental from rapid use, could make one die softer than the other. I am no metallurgist and wonder if the question has been addressed by someone who understands the process. Also, the
reverse was the die struck by the hammer so it might be more apt to being deformed compared to the anvil. To find an
obverse clash, I would look for an issue where the
obverse was the top die. There are some Antonine bronzes that I suspect were made with the
obverse on the punch but I have so little experience with them that I would not expect to have noted a clash. We also have to allow for the possibility that some
mint authorities may have
had different rules for when a die was retired and may have been more tolerant of die damage to reverses than to the
portraits. My page makes it pretty obvious that Severus'
Rome tolerated
reverse clashes with no problem. I don't know if the fact that I have seen so many relates to laws of physics, the
mint practices or the fact that I have examined 20 times as many Severus/Domna coins as I have any other emperor. Further, I am at a loss how we are to determine that the lack of
obverse clashes is the result of their never having existed or the possibility that they were not tolerated.
Numismatics is a study requiring expertise in
history, art and science. People equally expert (at a high level) in the three are
rare.
My apologies for the horrid photos on that page. They date from the time I was sensitive to the number of my readers who
had dial up access and made more compact images than I would today. Perhaps I should reshoot and replace but I don't even have access to my pages anymore to upload changes if I made them.