Coinage and Portraiture

Following on the previous post, I'm often struck especially with female rulers at the distinctive differences in conventional imagery between portraits (painted and/or bust - or even mosaic, the more I look at of that form) and royal images on coins.  Female rulers who may be portrayed stylistically or idealized in other portrait forms often come across in coin reliefs looking very different indeed from the more widely seen imagery from their rule.

Image:  Romancoins.info
Amalasuntha as queen regnant

I'm fascinated by this difference, which spans MANY centuries indeed.  To the modern eye, the coin portrayals appear both cruder and "uglier" by our standards, and it seems clear there must have been some sort of purpose in the portrayal of women as heftier, stranger, less idealized than in other media.

Image:  vroma.org
Cleopatra bust

Image:  LA Times
Cleopatra coin

It seems likely that the literal currency of coin portraiture made these images important as a way to send a message about female rulers; did it undermine the prejudice against a woman in power to reduce her feminine appeal?  Some images appear positively masculine - Elizabeth I's coinage has always seemed to me so contradictory to her painted portraiture, in fact giving an appearance of corpulence which, whether accurate to her appearance or not, tends to recall powerfully (literally) her father's image.

Image:  Wikipedia
Elizabeth I - The Darnley Portrait

Image:  Coins-of-the-UK.co.uk
Elizabeth I coin

If anyone knows of a paper looking into the portraiture of currency, especially of female rulers, I would love to know about it.  This idiosyncrasy has interested me for years, but I've never actually researched it.