I'm recently trying my hands on brewing green teas in a gaiwan and thought about the following: I always read one should put hot water in the empty gaiwan for preheating, which is no problem for the first brewing. But if you don't follow the first one right with the second etc, the gaiwan of course cools down. Now you have the leaves in there and can't preheat from inside. I tried preheating by putting the gaiwan in a bowl with hot water, but that's a bit complicated to do all the time.
I meassured the water temperature and it seems to drop about 15 (!) degrees from the boiler to the gaiwan, the porcelain really absorbs a lot (or lets escape a lot). I've got a boiler where you can set the temperature to 60, 80, 100°C. So couldn't I just heat the water to 100°C and shortly after put it in the gaiwan, when it's still maybe 90-95°C? It would then immediately drop to the desired ~80°. I'm just not sure if it would damage the leaves. Maybe if you are experienced you could try to drop the water on the walls of the gaiwan and let it drip down and cool a bit off on its way. Of course I simply can try
This would also be interesting concerning darker teas in pots, especially yixing. Since the clay does not conduct the heat very well, I imagine it would be hard heating the pot from outside after the first brewing.
Generally I'm wondering about some temperatures people mention sometimes. As even clay seems to absorb a bit at the beginning, it's almost impossible to get around 95°C or even above.
Maybe I'm making this a bit more complicated than it is, but I guess this forum would be the right place for such a discussion