You're not going to have any luck melting platinum in a typical gas crucible furnace. The melting point of Pt is 3215 F. With a natural gas furnace, for practical reasons, the upper limit is about 2300 - 2400 F, and that's difficult to obtain. Unless you spend a lot of money, the highest temperature rating of common refractory is about 3000 F. I know from experience that SiC crucibles can soften at white heat.
There are basically 3 ways to melt platinum: resistance melting, induction melting, and torch melting. As I recall, Ms. Hoke's daddy developed the first practical torch to melt platinum. It was called the Hoke torch and it is still sold. I think it originally used H2/O2 and some sort of lime melting dish for platinum.
Here's a chart of temperature colors that I posted earlier. I took it from a fire assay book. Note that white is about 2200 F and above. When the furnace and what's in it turns white, you can barely see the crucible. It's very hot to work around white heat and, with even a medium sized furnace, protective aluminized clothing is needed.
APPROXIMATE FURNACE TEMPERATURE COLORS
Lowest red visible in the dark.......... 470 C ..... 878 F
Dark red, blood-red....................... 550 C ..... 1022 F
Dark cherry.................................. 625 C ..... 1127 F
Cherry-red, full cherry................... 700 C ..... 1292 F
Light red....................................... 850 C ..... 1530 F
Orange......................................... 900 C ..... 1652 F
Light orange.................................. 950 C ..... 1742 F
Yellow........................................... 1000 C ... 1832 F
Light yellow................................... 1050 C ... 1922 F
White.................................... 1150-1200 C ... 2102-2192 F
