There's plenty of info on the web and ebay is also a great source of current marble values. The real valuable ones are the handmade late 19th C from Germany I've found. I found one in a dump area behind my house, It's pretty beat up from years of a plow going over it and it's small so it's not worth much, but it still was something cool to find. It's called a Latticino and it's like a tiny piece of art glass. I also found some clay marbles in the same area. everything in my hand here I found by eye in the corner of a wheat field by an old coal camp except the arrow head, which I found in a mountain pass area of Colorado.