Looks very good rendering to me
The painting on shield was done in those time "free handed" with mineral and or vegetal colors
Must absolutely not look as a Raphael painting, but like you have rendererd it
I know, the"russian school" show shields or pavese, antiquity or medieval as if they where painted by Rembrand or Raphael, and I always admire the result, jaws droping, but they didn't paint that way in those times . And the artists painting on shields and pavese were not the top of their time either, nobody could have afford their prices .
I like very much what you have done