I’ve never measured the temperature but with these fans, I placed approximately 3/8” - 1/2” deep very fine sand into my pan and heat over a burner. I place my hand, open palm, down just above the pan and it’s hot. Very hot. Like checking a grill. Place the segments in the sand as desired and then check every few seconds or so. Us a pair of needle nose pliers or as I do a long pair of tweezers. There’s somewhat a learning curve as you don’t want too much shading at the point of the fan. If so it just looks too dark.  After I remove all the segments I touch up with a block plane to balance the shading. To help with the balance of the shading, I will place the segments in the sand at an angle, ensuring the point end doesn’t go too deep into the sand.  The pictures below are not the same box, but are the same methods concerning the shading. 

Steve Gaskins