Another thing that is really helpful is go to a shop that deals in antique glass, tell the seller that you're learning and ask if he has a couple of old pieces that it would be OK for you to pick up and examine. Tell him/her what happened with the bird and that you'd like to be able to touch/feel some antique examples. There are some really subtle differences in old glass pieces. Pressed glass which is rolled out and pressed into a mold has a very different feel and subtle warps and wobbles to it that you don't see in modern glass. But you can really feel it when you touch it with certain types of glass. Others it is really hard to tell!