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NaOH and hidden superfat

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ThePopeOfSoap

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I recently read that Soapcalc assumes the NaOH that one uses is 100% pure. I’m using 98% pure NaOH, so am I correct in assuming that I’m actually adding an additional 2% superfat just by using this 98% pure NaOH? If this is true then new soapers should really be aware of this.
 

DeeAnna

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Yep, that's right. I've been sharing this fact for years, but I've not made a crusade of it. Most if not all soap recipe calcs have been that way at least until recently, so it's nothing new. Even older instructions for hand calculating don't correct for purity. Bear in mind the numbers we use for saponification values are averages, not precise numbers, so there's always some imprecision in the calculations.
 

ThePopeOfSoap

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SaltedFig

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The majority of my research has been about oils and their fatty acids, it’s probably time to take a closer look at NaOH. I wasn’t aware of its hygroscopic property.
The most fun way to explore the hygroscopy of our hydroxides is place a small bowl or curved dish on your scales, tare it (so the dish isn't counted) and then pour out a small pile of your hydroxide into the middle.

Note the weight. And watch.
It literally will soak up moisture in front of your eyes, and you'll be able to see the weight increase.

It's worth making a hydroxide puddle, just once, to see how fast it happens ;)
 

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