54 minutes ago, weinoo said:
By the way, I've seen a similar vessel (Chinese sandy pot) being used over some pretty high flames.
Yes. I've been using this sand pot (沙锅 - shā guō) for over ten years now.
I got through a few before I worked out how to look after them. No sudden changes, as you say, though they do take a high flame when asked to. That said, for most applications I use medium heat.