Re: Prussian "o-rings".
The Oilskin cover, which Prussians always wore in the field, is glazed cotton, with a leather cockade sewn on:
these became the mark of units, like the 6th , which had been on the Russian 1812 campaign as part of Yorck’s Corps.
To see more of these beautiful figures and how they were made, see:
http://www.accionunoseis.org/viewtopic.php?t=7349