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soap confusing!
I have run into this problem so many times since 1998 and I still am not sure how to handle it! I have seen soap formulas in old books to use to make shaving soaps using a combination of of KOH and NaOH. The authors have come up with different ratios of these two hydroxides but don’t always give you the numbers rather they will say 1/2 KOH and 1/2 NaOH or 2 parts NaOH to 1 part KOH. When they do calculate it sometimes they come up with the exact same numbers for both the KOH and the NaOH when they are saying it should be 1/2 and sometimes they don’t! As you know the molecular weight for each is different with a 1/1.4 (approx.) ratio.
What I want to know is:
Do I divide the oils (let’s say in half), calculate the SAP value of each half and come up with the different numbers for each half or is there a way to figure it out so that both KOH and NaOH come out to the exact number?
(Typically, I have always divided the oil phase into whatever ratio I needed and calculated the individual parts using the appropriate hydroxide)
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16 Replies
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I’m stumped, personally. Anyone else have any ideas?
As a result, I would fall back on what I always do whenever calculations are useless and/or incomprehensible (which is often).
Determine the correct value experimentally. Just make several batches with increasing levels of caustic, check the pH, and you have your answer.
As a byproduct of this discussion, I just realized why very many of the home crafters I’ve talked to are so overly hung-up on calculating things - it’s because it works very well for soap.
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if you’ve got a mixture of oils with different saponification values, the best thing to do is to calculate a mean saponification value for the whole mixture
you can do this by calculating (sap value x %weight) for each oil, adding them all up, and dividing the whole lot by the total percentage of the oils
here’s a worked example, with totally made up figures:
30% w/w oil A, sap value = 117 mg/g
21% w/w oil B, sap value = 20 mg/g
28% w/w oil C, sap value = 235 mg/gmean sap value = ((117 mg/g x 30%) + (20 mg/g x 21%) + (235 mg/g x 28%)) ÷ (30% + 21% + 28%)
= (35.1 mg/g + 4.2 mg/g + 65.8 mg/g) ÷ 79%
= 105.1 mg/g ÷ 79%
= 133 mg/g -
Run the soapcalc calculator twice? First with half the oils + KOH then with half the oils + NaOH. Then simply mix the NaOH with KOH and proceed as normal.
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Thanks for your responses!
I started out as a “soapmaker” and built my formulas by selecting oils by percentages then calculated the amount of sodium hydroxide and water by using either online calculators or a programmable calculator I own. After spending time on cosmetic chemistry message boards with chemists like the late Maurice Hevey and Perry I learned to work in formulas based on 100%. I have to admit that I still use these techniques for soapmaking but approach my liquid soap, shaving cream as a cosmetic chemist would using formulas based on 100%
I’m trying to make a “cold process” shaving soap which is no easy task because of the high and medium chain fatty acids used. I often go back to old cosmetic formulation books (which I don’t see mentioned very often here as a source) as well as old soapmaking books to see how it was done way back then! Because of the different ways they did things back then you’re more apt to come up with different approaches. I suppose that if I read more in the individual books themselves I might be able to figure out how the author works these things out.
Another issue that this brings up is the use of cosmetic chemistry books, soapmaking books, and going to places like the U.S. Patent Office and other World Patent Offices to find sample formulations to work with. I see mention of formulations from chemical supplier sites but no mention of these books from the last 100 years. With things like “brilliantine” and “pomade” becoming popular again why not look at those sources since many of them have several of these formulas listed!?!?
Thanks for everyone’s responses, I appreciate when everyone gives their time to share things and things in detail! I pretty much do what Belassi suggested and do it that way. It would be so much easier when reading a formula to know whether the author is working with the percentages of the oils or the percentages of the hydroxides when they write about shaving soap formulas!
Thank you!
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Hey, would this help?
http://www.soapguild.org/Certified-Lye/lye-calculator.php
https://www.thesage.com/calcs/LyeCalc.htmlThose calculators allow for simultaneous NaOH/KOH calculation. Did I get your problem right? Sorry, just reading briefly in a bit of a rush…
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BartJ,
Thanks so much! “the sage” is one of the older calculators out there but I’m glad to see that it has the NaOH/KOH option on it! Good to know!
I am a member of the Handcrafted Soap and Cosmetics Guild and I didn’t even know they had this calculator through Certified Lye!
The only problem with “the sage” is that it only lists “Stearic Acid” as their sole fatty acid on the calculator!
I just emailed Certified Lye and asked if they would include Stearic, Palmitic, Myristic, Lauric, Oleic and
Coconut Fatty Acid in their calculator! I hope they can!Thanks for your reply! How is everything in Poland?
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http://www.australiansoapmaker.info/ozcalc/lye.php
Nicer calc.Of course, I prefer mine…lol..
Determination of Saponification, Acid and Ester Values;Percentage of Free Fatty Acids and Glycerol in someSelected edible Oils: Calculation of concentration of Lye Needed to Prepare soap from These Oils
Equation to solve for NaOH and KOHFA
NaOH —KOH
Stearic 0.1411/ 0.1987
Palmitic,
Myristic,
Lauric,
Oleic
Coconut Fatty AcidMatch the numbers in the SEA soap calculator…gives the correct answer. You don’t need to read the fatty acid name…it won’t change the calculations..lol..
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Thanks,
The Aussie calculator only had a small percentage of available oils on it so it doesn’t provide what I need. Yours looks very complicated. I believe I would have to enter whatever percentage I wanted using KOH and enter the rest of the same oil again using NaOH and do that for every ingredient to get the totals of each hydroxide rather than just selecting a ratio of KOH to NaOH as the HCSC Guild does. Still it seems that I could get it work and get used to it although it doesn’t have an option or TEA on it so U would have to calculate that separately.
“Matching the numbers” should work but I’m thinking it would work for any other calculator as well so I am going to have to give it a try to see what I come up with! Thanks for sharing other options!
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I’m looking around again and checking out the online lye calculators and saw that MMS calculator offers a KOH/NaOH “blend” so that’s great but it also doesn’t offer the fatty acids as options. All of the others I had links to don’t offer that option.
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I spent the afternoon looking for SAP values of fatty acids then looking at lye calculators! (in-between customers) and found quite a few new sources and quite a range of SAP values! I made lists for the four ingredients and found several in a similar range and a few really off. I haven’t had to look at these for quite a number of years and was pleased to see some of the old ones still listed and quite a few new ones! The one that impressed me the most was “Soapcalc”. It has a ton of regular and exotic oils and all the “standard” fatty acids and the numbers seemed consistent and worked out mathematically just perfectly so I’m going with those. Sometimes it pays to go back and take a look at things even if they are things you work with on a daily basis!
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I have been using soapcalc for years, never have any problem.
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I heard back from Certified Lye and the calculator they have on the Handcrafted Soap and Cosmetic Guild, Inc. has a section called “Step 4” where you can add oils or fatty acids that aren’t listed in the calculator in “Step 2” and their SAP values and weight.
Between this:
http://www.soapguild.org/Certified-Lye/lye-calculator.php
and this:
http://soapcalc.net/calc/SoapCalcWP.aspI should be covered! Thanks!
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Soapcalc.net is just it for me.
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Hello David08848,
When I make all sorts of having soaps I use this calculator:
http://soapee.com/calculator
It has all basic acids and very simple at the same time.
Good luck! -
Vitalys, Thanks for posting this calculator! Nice to see one with all the fatty acids and the water percentage options!
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I make a shaving cream tha my husband loves, as well as my hairdresser, three boys, and two son-in-laws. They prefer it over a shaving soap. Easy on, razor glides, skin so smooth.
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