I’d come across this a couple years ago and it just resurfaced again last week on one of my favorite shows, MythBusters.
A common childhood pastime in Japan is making hikaru dorodango, or ‘shiny mud balls’ by taking a ball of mud and squeezing, packing and smoothing it, gradually drying it out, and slowly adding dry dirt to it, and finally rubbing it to a glossy shine.
The results are nothing short of amazing.
Looking at the process, it seems like what they’re ending up with is a packed, smooth ball finished with an outer layer of finely burnished clay particles, probably not far from terra sig.
Image from: http://www.kyokyo-u.ac.jp/youkyou/4/english4.htm , which also has instructions for making one of these little gems.
There is additional information and instructions here:
and at Wikipedia here: