I recently got a kiln dirt cheap and would like to try out sand casting using pure copper. I just wanted to know if anyone here has tried this?

I'd like to know more about copper casting if anyone can fill me in. I have a few days of reading behind me and no experience.

The sand: Olivine powder w/4% or more Calcium (Southern) Bentonite and 4% water.
Deoxidation: The Molten copper will be deoxidized with 15 percent phosphor-copper shot (1 to 4 granules per pound) and a little skimming. Correct me if you don't agree, i'm learning.

What I am unsure about is whether or not to pre-heat the kiln, pre-heat the kiln and crucible, or not pre-heat anything? It could take this kiln about an hour and 45 minutes to start melting the copper, my concern is that by throwing the copper in from the start I'm asking for additional oxidation. What do you think?