How do I clean lead-crystal glass that has a haze?

Short of having it acid dipped professionally, you can't!
The combination of the high temperature and acid chemicals in the washing medium attack the surface of the glass.
Wet newspaper and a hard scrubbibg or vinegar can remove mild lime stain from water in vases, but that is a deposit on, not an attack of the surface.
a few crystal companies will get them repolished as long as they really are lead crystal!

Stephen Pollock-Hill.
February 2009