I found a marble in my backyard as one of my first finds. It was found with several coins in a small pocket spill. Old marbles are often found and prized finds!
Hey littlebird..... you'll find marbles metal detecting because when you start finding coins, toy cars, etc. you're probably digging where kids used to play...hence you're likely to stumble onto some while digging for other targets... people find them in bottle/outhouse dumps too, as to why they end up there, I'm not sure..HH
Marbles are found everywhere, especially playgrounds and around houses. If you are interested in finding more of them, you can try screening them from around foundations. A friend of mine buys and sells properties, and he always digs and screens around the houses out to a couple feet. He has quite a collection of toys and many marbles from this method. He also screens around some of the big trees and bushes in the yards and has done well. I am lucky to be living right smack dab in the heart of our countries most prolific marble and glass making culture. I find lots of marbles, as well as cullet and scrap stained glass.
Marbles can be old, as many were brought here by immigrants from europe, with many being from Germany. Native Americans also made and used marbles in various games. Marbles are mostly glass, handmade as well as machine made. Some are made of clay and can have decorations on them and also some have a porcelain coating. Rarer still are marbles made of natural stone such as agate. Marbles can be worth a few cents each to many hundreds of dollars. There are marble books available, as well as websites online. We even have an annual marble festival here, that hosts competitions and collectors from all over to buy sell or trade. Contemporary artists give live demonstrations of the latest in marble making art and skill. It is an amazing thing to watch.
Hope this gives you some good info! Good luck!............HH