Stearic Acid Question

**drewmac** · 01-23-2011, 06:32 AM

So, I've been making my own shaving soap (more of a cream/soap) for a few months now and I'm getting differing opinions on the stearic acid I use in the product.

I use stearic acid in flake form from an online soap supplier. Directly on their website, they state it can be used in M&P soap bases, which is what I do.

The two statements I read over and over online are that stearic acid does or doesn't need to be saponified. Which one is it?

For the record, the same stearic acid product I use says it's safe for lotions, soaps, body creams, and lip balms. Stearic acid is also used in gum and margarine as well.

**mretzloff** · 01-23-2011, 07:30 AM

Originally Posted by drewmac

For the record, the same stearic acid product I use says it's safe for lotions, soaps, body creams, and lip balms. Stearic acid is also used in gum and margarine as well.

I think people think it is unsafe because of the word "acid", which is ironic because you cannot make soap without using acids (oils).

How exactly are you making this? Melting a melt-and-pour base and adding stearic acid to it will not work, unless you use lye at one point or another.

**drewmac** · 01-23-2011, 07:52 AM

Question answered via PM. Answer: Stearic acid is quite safe in appropriate levels.

**cymric** · 01-23-2011, 08:01 AM

If you obtained pure stearic acid then you do not need to saponify it. Saponification is ‘disentangling’ an ester (usually a triglyceride) into its constituents (usually glycerin plus the fatty acids). Stearic acid is such a constituent and thus cannot be saponified any further.

However, you should pay attention to a different issue. If you purchased stearic acid in acid form (C17H35COOH) then you need to add a specific amount of lye in order to remove the H and replace it with either a K or Na so that you end up with potassium or sodium stearate (C17H35COOK or C17H35COONa) depending on what you want your shaving soap to behave like. Otherwise you'll find that dissolving your soap is a bit ... well, difficult :). You may even want to purchase those salts directly from a supplier; to my knowledge there is not much of a price difference, and it saves you the trouble of the lye reaction and subsequent water removal. Perhaps it is even possible to perform this reaction in situ by melting the stearic acid and then carefully adding powdered lye pellets or concentrated lye solution—but for heaven’s sake be careful here. I’m writing this as a logical suggestion, not as a foolproof way of actually performing the reaction.

Of course you can leave in pure stearic acid for a bit of superfatting, but that is up to you.

**drewmac** · 01-23-2011, 10:37 AM

Got word back from the owner of the supply site I use, and she said it is perfectly safe in the quantities I am using (and even higher if I want).

19th test batch and 76 ounces (nearly 5 lb.!) of soap later and I think I've finally got it! I went in to this experiment with the goal of making a soap that was on par with both DR Harris and Soap Opera Himalaya soaps and it's really close.

**CaptainK** · 01-23-2011, 11:27 AM

Originally Posted by cymric

If you obtained pure stearic acid then you do not need to saponify it. Saponification is ‘disentangling’ an ester (usually a triglyceride) into its constituents (usually glycerin plus the fatty acids). Stearic acid is such a constituent and thus cannot be saponified any further.

First of all, let me categorically state that I am no expert. However, I have been learning to make soap, and the soap making process, and this just doesn't sound quite right to me.

I thought saponification did both the 'disentangling' (I like that word

) of esters into glycerin and fatty acids (of which stearic acid already is, so it doesn't need the 'disentangling' phase), and it reacted with those fatty acids to produce the salts (i.e. "soap molecules," e.g. sodium tallowate, sodium cocoate and, for stearic acid, sodium stearate - if sodium lye is used as the base).

However, you should pay attention to a different issue. If you purchased stearic acid in acid form (C17H35COOH) then you need to add a specific amount of lye in order to remove the H and replace it with either a K or Na so that you end up with potassium or sodium stearate (C17H35COOK or C17H35COONa) depending on what you want your shaving soap to behave like.

Yeah, that - the 2nd phase of saponification. If you're making CP soap and you add stearic acid to your fats/oils, if will saponify into sodium or potassium stearate, right?

Like I said, I'm new to this, but ... where is my understanding lacking?

You may even want to purchase those salts directly from a supplier; to my knowledge there is not much of a price difference, and it saves you the trouble of the lye reaction and subsequent water removal.

This is the route I'd go if I wanted to add sodium or potassium stearate to an M&P soap. It just sounds safer to me.

Curious - I know that each fat/oil brings its own characteristics to a soap - what qualities does stearic acid bring?

BTW, drewmac, are you planning on marketing your soap? Do you need testers?

**cymric** · 01-23-2011, 12:35 PM

Originally Posted by CaptainK

Yeah, that - the 2nd phase of saponification. If you're making CP soap and you add stearic acid to your fats/oils, if will saponify into sodium or potassium stearate, right?

No. Saponification is officially de-esterification under the influence of lye, resulting in glycerin and a fatty acid ion; in case of stearic acid C17H35COO-. Note the minus: the ion is negatively charged, as it should be, for at the beginning of the reaction we have neutral triglyceride and OH- ions. Afterwards we have neutral glycerin and water, and thus something else has to carry a negative charge. The saponification is now done.

Then, upon evaporation / decanting / ... of the water, the positively charged potassium or sodium ions of the lye (K+ or Na+) combine with the negatively charged stearate ions to form a solid. That's a different reaction called salting out (heck, crystallisation will do as well). If you're making soap then the two invariably follow each other, but they are in effect two different steps.

Curious - I know that each fat/oil brings its own characteristics to a soap - what qualities does stearic acid bring?

The ones you want in a shaving soap. It makes the lather dense and heavy. There's a thread about determining how quickly Martin de Candre is used up right now, and it features various pictures: the thickness is largely due to the stearic acid.

I don't even think you can make a useful shaving soap without stearic acid.

**komodo** · 01-23-2011, 01:03 PM

It might be interesting to play around with ions. Potassium already produces a softer soap product than sodium does. Magnesium would produce a soap where two carbonchains are combined with one ion, producing something that in itself as very good lubricant. Magnesiumstearate is used to lubricate tablet machines to make sure the tablet comes off the machine and doesn't stick to the punch of the rotary tabletting machine.

**drewmac** · 01-23-2011, 01:08 PM

Originally Posted by cymric

No. Saponification is officially de-esterification under the influence of lye, resulting in glycerin and a fatty acid ion; in case of stearic acid C17H35COO-. Note the minus: the ion is negatively charged, as it should be, for at the beginning of the reaction we have neutral triglyceride and OH- ions. Afterwards we have neutral glycerin and water, and thus something else has to carry a negative charge. The saponification is now done.

Then, upon evaporation / decanting / ... of the water, the positively charged potassium or sodium ions of the lye (K+ or Na+) combine with the negatively charged stearate ions to form a solid. That's a different reaction called salting out (heck, crystallisation will do as well). If you're making soap then the two invariably follow each other, but they are in effect two different steps.

The ones you want in a shaving soap. It makes the lather dense and heavy. There's a thread about determining how quickly Martin de Candre is used up right now, and it features various pictures: the thickness is largely due to the stearic acid.

I don't even think you can make a useful shaving soap without stearic acid.

Originally Posted by komodo

It might be interesting to play around with ions. Potassium already produces a softer soap product than sodium does. Magnesium would produce a soap where two carbonchains are combined with one ion, producing something that in itself as very good lubricant. Magnesiumstearate is used to lubricate tablet machines to make sure the tablet comes off the machine and doesn't stick to the punch of the rotary tabletting machine.

You both just made my brain hurt

**CaptainK** · 01-23-2011, 02:23 PM

Originally Posted by drewmac

You both just made my brain hurt

I find it fascinating - learn sumpin' new ever'day!

**Malaspina** · 01-23-2011, 02:33 PM

Originally Posted by cymric

Perhaps it is even possible to perform this reaction in situ by melting the stearic acid and then carefully adding powdered lye pellets or concentrated lye solution—but for heaven’s sake be careful here. I’m writing this as a logical suggestion, not as a foolproof way of actually performing the reaction.

PLEASE DO NOT DO THIS
If you are working with lye in any way, shape or form, please do some research on how to use it. It is an extremely reactive chemical and when not handled correctly can give you serious injuries. If you understand how to use it and treat it with respect it's fine. But make sure you understand what you can and cannot add it to.

**drewmac** · 01-23-2011, 03:02 PM

Originally Posted by Malaspina

PLEASE DO NOT DO THIS
If you are working with lye in any way, shape or form, please do some research on how to use it. It is an extremely reactive chemical and when not handled correctly can give you serious injuries. If you understand how to use it and treat it with respect it's fine. But make sure you understand what you can and cannot add it to.

Most certainly not...not messing with lye at all.

**SiBurning** · 01-23-2011, 03:05 PM

I'm more puzzled by the magnesium stearate. Why put bath tub ring in a shaving soap? Isn't this what makes lather hard to lather?

**Darjeeling Express** · 01-23-2011, 03:44 PM

Well when its ready for beta testing, please put me on the list. Quite a project. Himalaya and DH, two of my favorites! Congratulations.

**SliceOfLife** · 01-23-2011, 07:20 PM

Free stearic acid is used as a hardening agent in soaps and cosmetics. This is what you are getting by adding it to a completed soap.

Sodium Stearate or Potassium Stearate is Stearic Acid reacted with NaOH or KOH. This reaction produces these soaps (Creamy lathering soaps with little bubble, rather harsh on the skin) and glycerol.

Unless there's unreacted Base (Not sure what all bases would work, I'm only aware of Potash and Lye being used for this) in your soap, you will see little if any X-Stearate production.

If stearic acid can not be saponified, then literally hundreds if not thousands of soaping resources who list a saponification value for it are horribly, horribly mistaken and have been the cause of countless gruesome chemical burns. May God have mercy on their souls.

Cymric: Salting out is the process used to separate soap from glycerol. Usually with salt (NaCl)... hence the name. Saponification is the entire process involved in making soap. Salting out is a further optional step.

**komodo** · 01-23-2011, 08:40 PM

Originally Posted by SiBurning

I'm more puzzled by the magnesium stearate. Why put bath tub ring in a shaving soap? Isn't this what makes lather hard to lather?

Bathtub ring is not mg stearate, but a combination of mg and ca salts, primarily calcium and magnesiumcarbonate, and a few others.

It was a mere suggestion to play with the hardness of the soap by variating the ions you use. Making a pure sodium stearate soap will produce a very hard, aggressive soap. Adding potassium already softens it, at least with regard to the hardness. Magnesium stearate could function as a lubricant, or as an emulgator on small quantities. I am not suggesting to make a pure msgnesium soap, but i wouldn't want to use only sodium either. By the way, it is important in eye shadow production too.

**Jethro1984** · 01-23-2011, 09:10 PM

I wouldn't mind being a guinea pig for beta testing when it is available.

Sounds like an interesting process to say the least. I believe I should take notes in this class...

**SliceOfLife** · 01-23-2011, 10:09 PM

Originally Posted by komodo

Bathtub ring is not mg stearate, but a combination of mg and ca salts, primarily calcium and magnesiumcarbonate, and a few others.

It was a mere suggestion to play with the hardness of the soap by variating the ions you use. Making a pure sodium stearate soap will produce a very hard, aggressive soap. Adding potassium already softens it, at least with regard to the hardness. Magnesium stearate could function as a lubricant, or as an emulgator on small quantities. I am not suggesting to make a pure msgnesium soap, but i wouldn't want to use only sodium either. By the way, it is important in eye shadow production too.

A mix of Na and K works well for me. It depends on the fats involved in the soap but in the range of 50/50 to 66/33 seems best (Na/K)

**SiBurning** · 01-24-2011, 05:42 AM

Maybe if I said soap scum... Point is, the magnesium and calcium salts are all relatively insoluble. I was wondering how you make soap with these kinds of insolubles, and if you did, how the ions would affect the lather.

**komodo** · 01-24-2011, 05:54 AM

Originally Posted by SiBurning

Maybe if I said soap scum... Point is, the magnesium and calcium salts are all relatively insoluble. I was wondering how you make soap with these kinds of insolubles, and if you did, how the ions would affect the lather.

This is exactly the kind of question you might answer by actually doing it. I have a pharmaceutical background, I like to experiment ;-)