Sterling Silver Sterling silver is an alloy of silver and copper (92.5% silver and 7.5% copper) that is the standard for most silver jewelry.			Gold Fill Gold fill wire is a 12K gold tube that's filled with brass. The total thickness of the gold is 1/20 the thickness of the wire - a sturdy layer that will not wear off the way that low-quality gold plating does.
Copper I'm still questing for the perfect wire. I've discovered that pure copper isn't capable of holding a temper as springy as half hard sterling. Research continues...			Jewelry Brass These rings are a lovely golden color (not "brassy" at all), just a shade darker than the gold fill rings. Unlike the gold fill these brass rings WILL tarnish, but a few minutes in the tumbler shines them up very nicely.
Solder Core Sterling These rings have a thin thread of solder running through the center of the wire, meaning that if you want to solder your work you don't need to apply any external solder, just close the ring snugly and heat it. Flux is still recommended for minimizing firescale and helping the solder to flow.