> I am also polishing a 8 Inch mirror, but I am having problems with my
> channels closing on
> me after 30 mins. Can anyone help
How wide are your channels -- if they are not _at least_ a quarter of an inch wide, they need to be.
Have you tested the hardness of your pitch? If you are starting with sufficiently wide channels, it sounds like it is too soft at the temperature at which you are working. Try working somewhere consistently cooler (a consistent temperature helps!), or harden your pitch by boiling off some of the volatile content (WARNING: the volatiles are flammable!).
Clear Skies, Steve <sft@aegis1.demon.co.uk>