The image above is of marbles in their excavated condition from the 15th/16th century. Marbles appear to have existed for as long as people were able to find smooth, rounded stone. Slightly more sophisticated version came about with the development of clay marbles and even rarer, but more highly prized, carved agate marbles.
The picture below is my attempt at marble production; round balls of clay weighing approximately 15g each. The plan for these is to leave them dry for at least a week, then to colour then using pigments dissolved in shellac; chalk for white, charcoal for black, and the third colour I have decided on yet. Perhaps umber for a yellow or a ground up dried berry type to give a red. I'll be avoiding blue and purple as they weren't easily producable colours in period.
In the mean time, I've started working on some pennant banners. My pounding head is telling me I'll get no more done than cutting the fabric this evening, but at least it's a large chunk of the work started. Given that I making these as a "quick and dirty" version, I've cut the banners with a pinking shears which saves me from a) having to hem the fabric and b) effectively doubles my fabric as I won't have to double up the pieces either.