What (besides water) makes a soap rinse off more or less easily?

[paragon]

I noticed some liquid hand washes can be rinsed off much more easily than others. I know they were not 100% soap nor are they the type of soap most of us are making, but I assume the issue is still applicable to NaOH bar soap. What characteristic of soap determines whether it can be washed off of your hands in two seconds or ten? I've made a few batches of bar soap and will make more, but I would like to optimize the ability to get soap off of my hands quickly.

Let's assume it's not lye or carbonate heavy, since I store my lye well and my soap is finished enough to wash my tongue. (Obviously strong bases make skin slick and are hard to wash off, but I don't think that's the problem.)

 

[Michele50]

Do you have hard water or soft water....maybe hard water with a softening system in your home? My reason for asking is due to the fact that our son's home has hard water (well system) so they have a softener system; their dishes in the dishwater are always slippery. After they got a new one I thought, "great, no more slippery dishes!" WRONG and it is due to their soft water system. I assumed it was just the dishwasher but then I did some research and found the material below. A good read and it all makes sense. It might not be your case but I wanted to share it.

https://www.thoughtco.com/difficulty-rinsing-soap-with-soft-water-607879
"Do you have hard water? If you do, you may have a water softener to help protect your plumbing from scale buildup, prevent soap scum, and lessen the amount of soap and detergent needed for cleaning. You've probably heard that cleaners work better in soft water than in hard water, but does that mean you will feel cleaner if you bathe in soft water? Actually, no. Rinsing in soft water may leave you feeling a little slippery and soapy, even after a thorough rinsing. Why? The answer lies in understanding the chemistry of soft water and soap."

The Hard Facts of Hard Water
..Two factors contribute to that slippery-when-wet feeling you get after soaping up with soft water....

Chemical Reaction
...The sodium or potassium in soft water makes it much more unfavorable for the sodium stearate to give up its sodium ion so that it can form an insoluble compound and get rinsed away. Instead, the stearate clings to the slightly charged surface of your skin. Essentially, soap would rather stick to you than get rinsed away in soft water.

Addressing the Problem
There are a few ways you can address the problem: You can use less soap, try a synthetic liquid body wash (synthetic detergent or syndet), or rinse with naturally soft water or rainwater, which probably won't contain elevated levels of sodium or potassium."

We have naturally soft water and have no problems with dishes from dishwasher or rinsing after washing as we do at their home.

 

[paragon]

I am comparing multiple soaps in the same sink/shower, so the water is not a variable. But to answer you anyway, yes I know what hard water feels like, and no I do not have it. However I don't know exactly how my city conditions water before it gets to the home.

Still, that quote you provided might be moving in the right direction, since nearly all water has minerals/ions in it.

But again, water is not a variable. I am asking with the same water, what makes some soaps harder to rinse off? I gather one factor is solubility: soluble soap will make you use too much, so it will take more time to rinse away.

 

[Michele50]

@paragon, I have to admit that I do have a few soaps that I've made that did seem less easy to rinse off. I wonder if it has anything to do with the fatty acid composition (??), some are more soluble--making water 'wetter' and bla, bla, bla.

Edited: Just washed with a high coconut oil soap and it took a while to rinse off the slipperiness. I think I'll look over my recipes and pick out some bars with higher CO and compare these to those with a lesser % to see if those with less rinse off better.

 

[Zany_in_CO]

I gather one factor is solubility: soluble soap will make you use too much, so it will take more time to rinse away.

Hello, Paragon and WELCOME! When you get a moment, please introduce yourself to the group in an Introduction Thread. Include info about your soaping experience so we can connect with you at that level. Also whatever else you would care to share. I lived in HK for a few years -- loved it! I'm following the current political uprising with great interest.

What you said above makes sense to me. This is @DeeAnna's area of expertise. Hopefully she'll be along shortly to respond to your thoughts.

That being said, I don't know the chemistry involved, but in my experience with liquid soap, the answer to your question is, "the perfect measure" i.e., the correct ratio of water to soap during the dilution phase. This varies according to the type of oils used:
High in coconut oil: 40% soap to 60% dilution water
High in olive oil: 15% soap to 85% dilution water
You know you've reached the perfect consistency when the batch forms a film on top. Add a bit more water to absorb the film and you're there -- and it doesn't matter what oils I use, it rinses off easily.

NOTE: Liquid soap is watery. It's just the nature of the beast. As a result, some soapers prefer to dilute just to a point where the viscosity suits them, which means, a fairly thick result which means more soap than necessary is going down the drain when rinsing off.

In the case of 100% OO LS, 15% soap to 85%, the result is a very thin watery soap, but it has excellent lather. It can be thickened with brine.

 

[Michele50]

Hello, Paragon and WELCOME! When you get a moment, please introduce yourself to the group in an Introduction Thread. Include info about your soaping experience so we can connect with you at that level. Also whatever else you would care to share. I lived in HK for a few years -- loved it! I'm following the current political uprising with great interest.

What you said above makes sense to me. This is @DeeAnna's area of expertise. Hopefully she'll be along shortly to respond to your thoughts.

That being said, I don't know the chemistry involved, but in my experience with liquid soap, the answer to your question is, "the perfect measure" i.e., the correct ratio of water to soap during the dilution phase. This varies according to the type of oils used:
High in coconut oil: 40% soap to 60% dilution water
High in olive oil: 15% soap to 85% dilution water
You know you've reached the perfect consistency when the batch forms a film on top. Add a bit more water to absorb the film and you're there -- and it doesn't matter what oils I use, it rinses off easily.

NOTE: Liquid soap is watery. It's just the nature of the beast. As a result, some soapers prefer to dilute just to a point where the viscosity suits them, which means, a fairly thick result which means more soap than necessary is going down the drain when rinsing off.

In the case of 100% OO LS, 15% soap to 85%, the result is a very thin watery soap, but it has excellent lather. It can be thickened with brine.

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My bad, I didn't see the word "liquid" before @paragon "liquid" soap question. I've had some bar soaps feel more slippery than others and kind of wondered, myself, as to the whys.

 

[paragon]

I didn't realize how unclear I made my post! I actually did mean to ask about hard soap, despite mentioning liquid hand wash as a reference to describe the issue to be solved.

And I've now introduced myself here

 

[Zany_in_CO]

I didn't realize how unclear I made my post! I actually did mean to ask about hard soap, despite mentioning liquid hand wash as a reference to describe the issue to be solved.

I got that... I just don't know the answer re: hard bars, so I explained about rinsing off liquid soap which is where I have more experience.

Thanks for the intro... interesting to hear about the other things you've made. Waaaay beyond my wheelhouse or skill set.

 

[Michele50]

@paragon Your posing of this question has gotten my curiosity up because I also noticed that some of my bar soaps took longer to and required more water to rinse after handwashing. Today I changed up my ‘usual’ routine of handwashing to see if doinng so would make rinsing quicker and require less water—it did. Wow, big difference. Lol, now I can use both less soap and much less water.

What I did this morning: I held a dry bar of soap in my hand that I knew required more water and time in my hand. I placed them under running water. After hands and bar were wet, I moved them out from under the running water. I proceeded to flip the bar over twice to equal one full turn and then set the bar down. I kept my hands out from the running water and rubbed palms together, allowing fingers to glide between each other to build lather. After initial lather building, I allowed just my fingertips to quickly hit the running water to ‘load’ a small amount of water to the existing lather. I continued to build lather by quickly rubbing hands, ‘loaded’ a bit more water and then rubbed backside of hands and wrists and had plenty of foamy lather which I find delightful. In rotating the bar only one full rotation instead of my ‘usual’ four times did cut down how much soap I applied to my hands; thus, requiring less water and time to rinse.

Knowing that lauric acid is more soluble than other fatty acids, I knew that this is the reason coconut oil in soap both is quick to lather and creates a nice bubbly foam; but where I hadn’t applied this knowledge to was bar rotation (soap loading). I also knew that since we had naturally soft water (as you have) and not hard water with a softening system that replaces ions that this wasn’t the reason for my soapy phenomenon regarding certain bars of soap I've made.

‘My’ conclusion: soaps with a higher amount of CO will only require bar rotation of one full turn while others having a smaller amount will require a bit more since the combined fatty acids will decrease the solubility of the soap—more soluble, less ‘loading’ required and less soluble necessitates more ‘loading’ or rotations. I might still be wrong on the "why(s)" but your query prompted me to run a test on my more ‘soapy’ soaps—tested 2, one with really high CO with a 20% SF and the other with considerably less but still higher than others. I know I’ve got a couple in which I used a very little CO, I’ll find and test them eventually.