I don't flux platinum at all as I was taught it did not need to be
Platinum does not need to be fluxed. However if you are sizing a
ring with stones in it (or other repairs on jewelry with stones) you
need to coat it with boric acid to protect the stones.
Does 1300 platinum solder melt at 1300 degrees F.?
NO it melt at 1300 degrees Celsius, which is about 2372 dregrees