the chemistry of soap

[CaliChan]

Is there any one that actually knows what happens chemically to your soaps after the initial 48 hour cure (aside from water evaporation) that causes the soap to be more mild?
This has been bugging me for months and i cant find any information on it.
I know that if i use my soaps before the 6 week mark they will completely dry out my skin and i just cant use them or my skin will crack.
I know that "safe" doesn't necessarily mean ready but what happens within the soap to make it ready?

 

[Lotus]

You know! You ask a good question. I have "non oily" dry skin, but I've never experienced a soap in my life that actually " dries out my skin," as so many people attest to. Once, I worked next door to a salon and they were kind enough to do a paraffin wax treatment on my hands. I wonder if this can somehow be effectively incorporated into soap. I'll look it up.

However, I work with polymer clay a lot. For some reason this gives me very severe cracked finger tips on my "working thumb." I'm wondering if my next batch will help with that.

 

[melstan775]

Soaps are like wine, they get better as they age. It takes some time for the pH to come down and the elements to meld together and water the evaporation means the remaining elements (the saponified oils) are harder, and when that happens, voila - soap and glory!

 

[DeeAnna]

Read Kevin Dunn's book _Scientific Soapmaking_. Keep a critical mind as you read, however. Some of Dunn's conclusions are a little questionable, but his book is interesting and enlightening if you like to read about science and soap.

The change during cure may be as much physical as chemical, by the way. I don't think there has been much study of the physical structure of hand made solid soaps, but some of the info Dunn provides in his book makes me think that a solid soap is organized in a layered structure much like the structure of clay particles in soil. Given what I know about the properties of clay in soil, this would explain why it takes soap weeks to "cure" after saponification is complete and explain why the properties of soap (lather, scent, mildness) change so much during that cure.

But this is only an untested hypothesis of mine. Without research and data, it's just a nice story.

 

[soapguy]

Basically, the process is this... and acid (the fats and oil) are mixed with a base (KOH or NAOH) and water. The resulting reaction will produce a soap and glycerin. If you look up the molecular structure of a fat and that of soap, you will be able to see what has occurred. Try Wikipedia for an in dept discussion on the subject.

 

[jcandleattic]

Basically, the process is this... and acid (the fats and oil) are mixed with a base (KOH or NAOH) and water. The resulting reaction will produce a soap and glycerin. If you look up the molecular structure of a fat and that of soap, you will be able to see what has occurred. Try Wikipedia for an in dept discussion on the subject.

I think the OP was asking what happens AFTER that chemical process has occurred. Not what the science is in the actual process of creating soap.
Every soaper should know the chemical process to create soap, but the chemical science of what happens after soap is soap to then further create a mild bar is as DeeAnna says, much of a mystery, because there isn't any (or it's very well hidden if there is) studies, with scientific data to explain it.

 

[soapguy]

I guess I still don't get it. The longer you cure the soap, the more lye is allowed to react with the fats When the process is complete there will be no more lye to react with the fats. With time, water will continue to evaporate and the soap will get harder. My thought is that these two factors will affect the PH of the soap. The closer you get to a PH of 7 the milder. Am I missing what is meant by milder? Or is it how soap cleans? Because, the latter is what has bugged me the most.

 

[soapguy]

Maybe short cured soaps dry the skin because of the excess glycerin. Glycerin is hydrophilic and will pull the moisture out of your skin. With age, the glycerin will pull it out of the air thus eliminating that problem. I might have to look into this roblem:

 

[jcandleattic]

I guess I still don't get it. The longer you cure the soap, the more lye is allowed to react with the fats When the process is complete there will be no more lye to react with the fats. With time, water will continue to evaporate and the soap will get harder. My thought is that these two factors will affect the PH of the soap. The closer you get to a PH of 7 the milder. Am I missing what is meant by milder? Or is it how soap cleans? Because, the latter is what has bugged me the most.

Most handmade soaps regardless of how long they cure will never get down to a pH level of 7. Most linger around the area of 9-10, and some, 10-11.
Even with HP soaps that you cook through the saponification, and presumably evaporate out the excess liquid, will be milder - meaning more gentle to the skin - after a full 4-6 week cure.
There is no scientific evidence or data to support this. However, in my own personal experience, I can pretty much tell when I am using a bar that has not been cured at least 4 weeks. It definitely will dry out my skin.
It could be as you said, the glycerin levels are higher during this time, however true saponification should only last 36-48 hours.

 

[soapguy]

I know what you mean by not reaching a PH of 7.0, but I has not stopped me from trying. I figure if Dove can do it, why can't I. My understanding is that they rebatch their soap in order to do it.

 

[dagmar88]

I know what you mean by not reaching a PH of 7.0, but I has not stopped me from trying. I figure if Dove can do it, why can't I. My understanding is that they rebatch their soap in order to do it.

The closer you get to a PH of 7, the farther you get from soap.

The main ingredient of Dove "soap" is Sodium Lauroyl Isethionate, a surfectant. That's why it's called beauty cream bar, instead of soap.

 

[soapguy]

The closer you get to a PH of 7, the farther you get from soap.

The main ingredient of Dove "soap" is Sodium Lauroyl Isethionate, a surfectant. That's why it's called beauty cream bar, instead of soap.

According the study below, there are five soaps with near 7.0 PH. Dove baby is at 7.0. At what point one stops calling soap by it's name I leave to marketing. I guess we can't always agree, but it has been interesting.

http://www.healthmegamall.com/articles/babeskinarticle71.pdf

 

[dagmar88]

According the study below, there are five soaps with near 7.0 PH. Dove baby is at 7.0. At what point one stops calling soap by it's name I leave to marketing. I guess we can't always agree, but it has been interesting.

http://www.healthmegamall.com/articles/babeskinarticle71.pdf

Actually, what is and isn't soap is very well defined by the FDA.

 

[jcandleattic]

According the study below, there are five soaps with near 7.0 PH. Dove baby is at 7.0. At what point one stops calling soap by it's name I leave to marketing. I guess we can't always agree, but it has been interesting.

http://www.healthmegamall.com/articles/babeskinarticle71.pdf

What dagmar88 said. The FDA regulations and ingredients used are what determine if what is made is a soap or not.
I don't consider Dove or really any commercially made "soap" soap.
Dove can get to that level of pH because their bars are not handmade, and are made with more harsh chemicals than the average handcrafter uses.

 

[soapguy]

Now I understand. To a "truist" a soap must be composed of an alkali and a fat. The FDA regulates cosmetics. If you make any claims on your soap regarding conditioning or moisturizing properties then it is a cosmetic, not a soap and will fall under their regulations. So technically if I add anything to my soap that is neither of the above, I may technically not have a soap. Yet, I can buy commercial products labeled as bar soap at any general store.

 

[bodhi]

Regardless of the FDA's definition, i think it should be common sense that soap is soap, and detergent or surfactant bars are not. (I know that is a stretch, but in a perfect world...) To make soap, you must saponify. Saponify or saponification are old terms derived from saponins. Saponins are naturally occurring chemicals that foam and clean. It may be a chicken and egg scenario, but i think the term was derived from the saponaria plant - also called soapwort. It foams and cleans as do all plants with good saponin content. We dont call them bars of dert or bars of surf, though i think those that are, should! We call them bars of soap, because thats what they are.

(as an aside, i find it rather amusing that a soap making forum, called soap making forum, has a spellchecker that highlights saponify, saponification, saponin and saponaria, lol)

 

[soapguy]

bodhi, I can agree with your post and definition of a soap. My problem is with the statement that the closer you get to a Ph of 7 the further you get from a soap. I know that soap will naturally have a ph greater than 7.0, but a soap maker should still be able to bring it down to almost 7.0 by adding a mild acid such as boric acid and rebatching the darn thing. It will still lather, and maintain it's soap properties. Anyway, I am sorry if this has turned into an argument. It was not my intention. I can get very intense when it comes to soap. No hard feeling people.

 

[bodhi]

Oh dont take my comment as an argument. I am just bothered that detergents can be called soap so often that people actually beleive they are really using soap. IMO if it is anything other than saponified oils, it is not soap and can have whatever ph it likes as long as it isnt identified as soap. I agree about the ph though and i wonder how low a bar of soap can get? I can get my liquids down between eight and nine but have never tried it with a bar. then again maybe i have. I make a bar with an odd formula but never bothered to check the ph. hmmm... can you check the ph of a bar with a meter?

 

[soapguy]

OK, though I still don't know how low you can get soap ph to go down, apparently others have tried to do it by cold process and have not succeeded to get it to seven. The results have been a box of sludge. It would be interesting to find out if they just over acidified their soap. I found a good discussion on this very subject back in 2010 on this site. I am going to have to buy a PH meter, I have access to hospital PH strips but need something a little more sensitive. Could it be that reaching the PH level of 7.0 is much like reaching the speed of light? The closer you get the harder it becomes to attain it.

http://www.soapmakingforum.com/f11/how-lower-ph-handmade-cp-soap-17696/

 

[bodhi]

Now you have me curious. I have a meter and a bar that may have a lower ph than average. Any idea how i would check with with a meter? (have soap and meter in hand now! )