Lye % make a difference?

[PatrickH]

Using Soapcalc.
My Sodium lye is food grade beads 99%
Does it make a difference in lye calculation in Soapcalc?
95% vs 99% I would think it would be a 4% difference when determining how much lye is being used or needed for a soap recipe?

 

[Kittish]

I couldn't find anything that stated an assumed purity of NaOH for calculations in SoapCalc. I sent them a message asking what value they use.

 

[PatrickH]

I couldn't find anything that stated an assumed purity of NaOH for calculations in SoapCalc. I sent them a message asking what value they use.

Ok, thank you. :bathtub:

 

[galanda]

The European Pharmacopoeia (Ph. Eur.) defines NaOH(White, crystalline masses, supplied as pellets, sticks or slabs) as not less than 97.0 per cent and not more than the equivalent of 100.5 per cent of total alkali, calculated as NaOH. I'm pretty sure US Pharmacopoeia has same or simmilar definition.

This means that everything in 97-100.5% purity range is considered analytical pure NaOH and will have no effect on any calculation. Anything out of this range is not considered pure NaOH. If you have NaOH pellets out of this purity range, don't use it because impurities can interfere with saponification.

Hope this is helpfull

 

[DeeAnna]

Um, let's slow down here.

First off, yes, the NaOH purity does affect the superfat in your soap.

But let's put it in perspective. The calculations we do to create a soap recipe are largely based on averages and estimates for all of the ingredients we use.

For example, you may not realize that the saponification values used in soap recipe calculators are all averages. The sap value of the actual fats you use in your soap can and do vary from the average sap value -- they may consume more NaOH or less NaOH, and that will also change your superfat.

And additives also affect the superfat. Did you know if you add milk to your soap, even non-fat milk, the superfat increases due to the NaOH reacting with the milk proteins? Or that adding any acidic ingredient can also increase the superfat because the NaOH reacts with the acid?

Second, Soapcalc and all the other online calculators I have checked are all based on 100% purity for the NaOH. See below for a work-around.

Third, you do NOT need reagent or pharmacological grade NaOH to make soap. Technical grade is fine. Tech grade purity runs anywhere from 90% on up. The NaOH I use is in the 95% range and it works fine.

Even if you insist on buying reagent grade NaOH, the purity of the NaOH will drop while you use it, simply from exposure to the carbon dioxide and water vapor in the air. This is especially true if if you don't handle and store the NaOH properly. Most of the impurities in any grade of NaOH are sodium carbonate (soda ash, washing soda) and water -- the normal impurities that come from NaOH being exposed to air. More info: https://classicbells.com/soap/lyePurity.html

***

You can adjust your calculations to account for the NaOH purity being less than 100%. The easiest way is to subtract the purity difference from your desired superfat and use that answer as the superfat setting in your soap calculator. Like this:

Purity difference % = 100 - (actual purity of your NaOH)
Superfat to use in your soap calculator % = Desired superfat % - Purity difference %

Example:
My NaOH is 95% purity
I want 3% superfat in my soap

Purity difference = 100 - 5 = 95%
Superfat for calc = 3 - 5 = -2%

Yes, you can set the superfat to be a negative number -- in this case I would type -2 in the box for the superfat

 

[galanda]

You are absolutely right! I'm not saying you can't soap with technical grade NaOH, as long as you adjust calculation it works fine. But, tech grade NaOH contains more impurities. Not only thay can alter saponification, but also those impurities have higher levels of heavy metals. Technical grade is good for unclogging drains and other industrial aplication but I would never use it in cosmetics. Heavy metals are toxic to humans, animals and ecosystem in general. I'm saying this as a molecular biologist and quality control analyst in pharma industry.