Before they could be made by machine, of course, marbles were very much more highly valued than they are nowadays. Hand-made marbles are still very collectible.

Here's a good page on valuable marbles, which also points out that the phrases "playing for keeps" and "knuckling down" originated in playing marbles:
http://www.irelandsantiques.com/articels/marbles.htm


It occurs to me that if you had a marble made out of marble, that would represent a lot of hard work by someone. To the extent that a hand-made marble was perfectly spherical that would make it especially prized.

We don't associate marbles with money, risk and gambling at all these days, but it's easy to see that once it would have been devastating to lose all your marbles.

Interesting that the USn usage of marbles phrases is slightly more wide-ranging than UK usage:
http://wordsmith.org/board/showthreaded.pl?Cat=&Board=wordplay&Number=15594