Nooooo! Don’t do it!
I watched a former bone headed boss of mine, against my advice, take
heat to a 13 plus carat golden sapphire. It turned clear and white
as glass. Most saphs today are heat treated and or filled and will
not survive a burn out and casting. The only stones I’d recommend for
this are synthetic saphs and untreated diamonds.
My former boss boss had to buy a 14 carat golden sapphire and have
it recut to fit the customer’s mounting. A very expensive fix.
Have fun and make lots of jewelry.