Hello / 2 soap chemistry questions

[mistepp23]

First of all, hello, this is my first time making soap. Now that that's out of the way, I have a couple of soap chemistry questions that I've been curious about.

1. The recipe I used had the following ingredients:
-Coconut oil
-Olive oil
-NaOH/H2O
-Lavender essential oil
-Oatmeal

I noticed that, about a day after I'd poured the soap into the mold, I noticed a moderately strong ammonia smell throughout the room. I'm just curious where the ammonia came from, and if I should pitch the batch.

2. Why is there a 3-week curing period? The soap seems ready now. What further chemistry takes place during this period?

Thanks so much!
-Michael

 

[IrishLass]

Hello Michael, and welcome!

I wouldn't worry about the ammonia smell at this point. The more you soap, the more you'll find that it's not unusual for new soap to give off a weird smell at first. Usually it has to do with foody additives such as milks, etc.... The off-smells usually disappear during cure.

Re: cure. Bar soap is safe to use as long as it is tongue neutral when the zap test is applied, but just be aware that "safe to use" does not necessarily equal "best time to use". According to Dr. Kevin Dunn (a chemistry prof) on page 79 of his book 'Scientific Soapmaking', three things happen during cure:

1) Soap loses weight as moisture evaporates
2) It hardens
3) Any leftover alkali is neutralized by atmospheric carbon dioxide

and on page 230 of the same book Dr. Dunn talks about how the pH of soap lowers during cure. He says that during cure, the acid carbon dioxide naturally present in the air slowly reacts with the alkalis in the soap, helping to neutralize them, and it is for this reason that aged or cured soap is milder than fresh soap. I should mention that when he uses the word, 'neutralize', Dr. Dunn makes it clear in his book that he does not mean the soap takes on a neutral pH of 7, but that it becomes 'tongue neutral'. Soap will always be on the alkaline side of the pH scale, but curing helps it to reduce to the lowest pH it can possibly reach for lye-based soap, which is usually between 9 and 10.5.

I like to cure my soap for at least 4 weeks. Six weeks is actually even better, but I've found that 4 weeks is when my soap is at its earliest best in terms of mildness, hardness, lathering abilities, and longevity. When used too much earlier than that I find that they are harsher to my skin, not as firm, they melt faster in the shower, and the lather is not up to par.


IrishLass

 

[Hazel]

Welcome!

 

[mistepp23]

Thanks for the great reply, IrishLass! You explained it very well. I never would have thought to lick the soap to test its readiness, but I'm glad someone did. I'm gonna look into the book you mentioned, because I like to understand why I'm doing something, instead of just following a list of instructions. I'll definitely be making more soap in the future.

Thanks again!
Michael

 

[IrishLass]

Glad to be of help.

IrishLass

 

[mistepp23]

Follow-up: It's been curing for only 3 days, but there was no "zap" at all when I put my tongue to it (I'm familiar with the 9V feeling), it just tasted like soap. is it possible that it's ready, already?

Thanks,
Michael

 

[IrishLass]

Yep- as long as it doesn't zap, it's safe to use. It probably won't be as wonderful as it will be in 4 weeks, but at least it won't burn a hole through your skin. :wink:


IrishLass

Edited to add- my soap is usually zapless right out of the mold if it went through the gel stage.

 

[mistepp23]

Ok, thanks. I'll leave it a few more weeks before I give it away to anyone.

-Michael