Hi Emery, the salts begin to melt at ~350 Deg F and are fully melted at ~400 Deg F. The melted mass then solidify when cooled down. Since I use dedicated containers, I just cover the container with Saran wrap held down with rubber bands. That keeps the salts clean and minimizes moisture absorption of the salts. Any water in the salts is dangerous when the container with salts is reheated. Any water in the salts can cause hot salt splatter when reheated. Nitre bluing salts left in closed containers can last years.
I have all the chemicals, hot plate and iron tanks for doing hot bluing, but a hot lye solution has safety issue that I have been reluctant to entertain. Maybe my next bluing job will be a real hot blue.
Regards,
Richard