Oooh a HPOP thread!
I suddenly realize how long it's been since I've made soap this way and now I feel like an old lady saying (imagine croaking voice) 'you know, back in my day we did like this...' but anyway, here's my 2 cents.
When I did ophp I made sure it went super slow (20min). I had an oven thermometer that I kept around 75C (sometimes boosting it to 100C for a minute in the beginning to get things going) by opening and closing the oven door, because 75C wasn't an option on my oven
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I think I kept everything covered with plastic wrap (sorry nature!) to avoid loss of moisture and waited until all was gelled. Gel doesn't necessarily mean saponification, but it does mean fluid batter. I normally used soy yogurt for fluidity, but I think j I've used sour cream once too in a pinch.
The most fluid batter I have ever had was with 25% lye concentration and alcohol extractions added after cook, but that was warp city. I think a fluid batter that doesn't warp is the holy grail of hp soap
Have fun!
Edit: ps. I used to love glass bowls for hpop, because they allow to see the progress of gell phase very accurately, but stopped using them out of fear they might crack.
Pps. I often preferred lower, wider bowls because I didn't have to open my oven all the way to see how the soap was doing, which kept the temp more constant.
Ppps. I've had the odd volcano, but as long as you keep yourself out of harms way, the worst thing that happens is your oven gets cleaned..
So don't go in trying to safe your soap if it's splattering all over the place, just shut off the oven and clean up later.