How can I dop opal for cabbing?
Green dop wax is best. Don't use glue. I read something about colour loss up there, god knows what they are on about this is untrue. Opal is relatively soft, treat it with care. 

To get the stone off again, leave it in the freezer for half an hour to harden the wax, it will pop off.

I grew up on the field in Lightning Ridge and found, cut and sold my first opal when I was seven years old. I have 35 years industry experience. I say this to give you a base line to judge the value of my advice against others who might say otherwise.