The Light Shades are available in various sizes for the bulb.
The opening is ground to a specific dimension for your needs. The Glass usually has a whiter light (cooler) or can be made with more yellow (warmer) underneath. They are available at Volta Gallery or at the Glass Shop across the street, next to where the glass is made. The wonderful thing about using these as a light-shade, is the outside of the glass is fabulous in their own right, but the added dimension of the light from within is magical.