the mask thing is more common to front guards like an additional chest / waist protector, though it does exist on should once too. I think most were painted to some degree. Here is a surviving painting from the Song dynasty http://i240.photobucket.com/albums/ff59/RollingWave/W020080229481316400499.j...

I think the general issue is that Chinese armor were typically controlled by a central government, especially higher quality once, and thus when one style fall out of use, they typically just destroy / melt the armors they hold on to. Armour isn't a particularly popular burial item in China. and the...