I gave up trying to use the tempil paint and rely on a dull red color with the lights out.
I purchased some Tempil paint years ago. Also stopped using it years ago. It never impressed me. Found it tedious and difficult to "read". Although it did, at a minimum, help confirm the duration of exposure in the propane flame necessary to reach annealing temperature. I now rely on the duration of time in the propane flame and visual confirmation of annealing.
I just finished annealing 3,500 .223 cases. I use a single propane torch and spin the cases by their case heads fastened into a Lee case head holding tool mounted in a battery operated drill. I place a battery operated clock on the table close enough that I can hear the seconds tick, as well as observe the second hand. 5 1/2 seconds of time is the norm for .223 case neck/shoulders based on my torch flame and length of flame. Some brands of brass are a little different than others, as some show the annealing discoloration a little sooner than others. And some (the minority - very few) hardly indicate annealing at all. On those I predominantly rely on time in the flame much more than annealing discoloration.
It requires a little longer to anneal 300 Win Mag and 7mm Rem Mag case necks/shoulders, compared to the .223s.
Here's a tip to beginners. Let the propane flame impinge on the case shoulder rather than the case neck, and let the heat from the shoulder conduct/transfer to the case necks to anneal the case neck. The case necks themselves heat much more rapidly in my experience. There's more forgiveness by focusing the intense flame on the shoulder area (more mass in shoulder than the necks) and allowing the heat to conduct across the case neck.
The case neck is the area we'd like to anneal most consistently, because it affects neck tension. If I overheat the shoulder slightly, no harm in that respect. In my studies and experience, there is some latitude built into the annealing time-temperature process which still produces an acceptable result. I just recently read an article that shows the temperature versus time duration to achieve case annealing. It's fortunate that this curve flattens across "time" within the range of effective annealing temperatures. Otherwise it would be like trying to anneal a case neck made out of candle wax. One instant no melt (no annealing) and the next instant, poof, no case neck (over annealed).
Practice on some "junk" cases. There is a little bit of art involved in the visual recognition of annealing case necks the way I anneal case necks. I primarily rely on the propane flame length, and duration of time in the flame. After I remove the case necks from the flame, I continue to spin the case shoulder on a wet sponge in order to bring the temperature down for safe handling rather quickly. The rate of cooling makes no difference/no affect on the annealing process. I cool them down on a water soaked sponge so I can handle the cases without burning my fingers much more quickly. And this method doesn't soak the interior of the cases in water. Water never enters the casings. Practice does improve skill level. I've been annealing for 10 years now. Having just annealed 3,500 cases over the past couple of months, I'm much better at it now than I've ever been in the prior 9 years.
Mikecr's method is an ideally controlled method of annealing, which should produce the utmost consistency. If the lead is molten, you know the temperature of the annealing bath is very tightly controlled, thus the temperature of the case necks also exceptionally uniform. Hats off to Mike. I've simply never had the gumption to attempt that method. I hate the idea of a molten lead burn/splatter.
Would be both interesting and educational to observe Mike's method in practice.