Is 600 degrees F right for platinum casting flask temperature? 

Yes. If you cast hotter the surface will suffer. Today’s centrifugal casting machines bring so much force filling is not an issue even at these low temperatures.

I’m getting some plaster cracking, how can I fix that? 

Docs is sensitive to moisture. Keep it dry. If humidity intrudes, dry the remaining powder for use. Thin steel flasks that show wear can be a cause of cracking as well.

How does Docs stand up to resin model expansion or delicate design elements so well?
It’s our binder. As a non acid collloidal binder it vitrifies at about 1500F to bring maximum strength.

Why is Docs harder to remove? 
See above.

Docs is expensive compared to some other plaster investments. How do I justify the cost?

Several ways. Same day casting brings enormous flexibility to the work schedule. The strength brings design flexibility. The smooth surface result even with high-temperature metals like extreme white gold and platinum is a huge time saver.