Is this right ? (Lye concentration)

[CecileBC]

I don't recall soap made with lye at 40% or higher concentration being zappy after a reasonable amount of time (18-24 hr). "Time to trace" and "time to zap free" are two different things in my thinking.

Hi DeAnna,
I was wondering about that actually. My first soaps were made with lye at 40% concentration, and after a week they still gave a tingly feel when I tried them under water. This tingly feeling did not last after a full 3/4 weeks' cure. Would that be considered a "time to zap free" ? (basic recipe with OO, Coconut, shea, castor ran through soap calc). Is some of the NaOh still "digested" during the cure ?

 

[DeeAnna]

Hi DeAnna,
I was wondering about that actually. My first soaps were made with lye at 40% concentration, and after a week they still gave a tingly feel when I tried them under water. This tingly feeling did not last after a full 3/4 weeks' cure. Would that be considered a "time to zap free" ? (basic recipe with OO, Coconut, shea, castor ran through soap calc). Is some of the NaOh still "digested" during the cure ?

I don't test my soap as you describe; I only use the actual zap test to confirm excess lye.

I don't have any way to know if there's a correlation between general skin feel and zap to the tongue. If there is a correlation between the two, I think several hundred years of soap makers would probably be using a skin test, not a zap test.

IMO, I wouldn't call 3-4 weeks as the "time to zap free" because you don't actually know if the soap was actually zappy.

 

[CecileBC]

I don't test my soap as you describe; I only use the actual zap test to confirm excess lye.

I don't have any way to know if there's a correlation between general skin feel and zap to the tongue. If there is a correlation between the two, I think several hundred years of soap makers would probably be using a skin test, not a zap test.

IMO, I wouldn't call 3-4 weeks as the "time to zap free" because you don't actually know if the soap was actually zappy.

Thank you DeAnna

 

[Tammyfarms]

if the Palmitic + Stearic is > 30%, which is about where I like my soaps to be. I've settled into a high lard + tallow recipe that works well if I start with the melted and cooled fats at around 85-90F, a tallow recipe that I like to start at 95-100F, and a soy wax recipe (GW 415; plus cocoa butter and/or shea butter) that I start at 110-115F. I usually have the lye at room temperature (70F). I let the fats cool down a bit more (-5F) if I know the FO or EO blend or an additive will cause acceleration or heating, and start warmer if I know the scent will decelerate.

Thank you @Mobjack Bay the information on temperatures is exactly what I have been wondering about. This is extremely helpful!

 

[Mobjack Bay]

I don't recall soap made with lye at 40% or higher concentration being zappy after a reasonable amount of time (18-24 hr). "Time to trace" and "time to zap free" are two different things in my thinking.

Assuming my thinking is anywhere reasonably close to correct, the rate of reaction would be slow at first due to the high (40%+) lye concentration. This would explain the longer time to trace.

But as some time goes on, there would be less and less interference with the remaining Na+ and OH- ions as more and more NaOH is consumed by saponification. So I'd expect the rate of saponification would return to "normal" rates when the NaOH concentration drops below that mysterious 40% concentration barrier.

The initial slow saponification step might only take an hour or three, depending on the soap temp and the fatty acids involved. Then back to business as normal.

It seems like a reasonable hypothesis anyway.

Thank you! This makes sense to me and is a good working hypothesis for moving forward.