Opalized Glass- What's it for?

Among a lot of stuff I bought at a garage sale this weekend I got 12 4x5 sheets of opalized glass and a mixed partial box of 8x10 sheets of opalized & ground glass. Can anyone tell me what they are for? I have a feeling they are for lighting, such as for a light diffusor or some such thing so I posted here.

Thanks,
Randy

They are for light diffusion, in various types of lighting situations.

Dave Parker
Satin Snow Ground Glass