Once it settles down though, both of these can be used up to at least 900 F in my experience, as I said above.
I believe you are correct.
I just ran a sample of it up to 930F, with no problems. So apparently potassium nitrate can be used alone for annealing at 800F.
Data trumps whatever we find on the internet, and we both agree. Most sources recommend temperatures in the low 700s for annealing, and I didn't realize you were working at higher temperature like I do.
Edited to add: There is one problem with pure potassium nitrate. When it cools, it expands. My sample is now solid again, and firmly jammed in the bottom of my heating cup. The 60/40 mixture contracts when it cools. It just cleanly falls out as a solid disk.
