Glass comes in so many forms and is made from a wide array of materials, such as sand, silica, sodium, limestone, calcium, and more. Sometimes it's factory turned, sometimes hand blown, and sometimes floated. The result is such a variety of shades and textures, often becoming kaleidoscopic effect when held up to the sunlight.
This collection contains old bottles, blown paperweights, elegant vases, and drinking glasses, which are often works of art in themselves.
For an overview of glassmaking, you might want to check out Kahn Academy's post.