Pure caustic soda ?

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allane

Well-Known Member
I bought a bag of lye and unfortunately did not realize it said 99% on the bag. I realized my soap which is normally superfatted at 10% did not feel the same way. I rebatched it and added 5% of shea butter. It feels the same like my other soaps, but i will not sell it. Is there a lye calculator that has 99% lye calculation ? Thanks.

Allane

If you want to be precise with the amount of soda you will need to gain a specific lye discount, you must do a few maths.

Say you have a recipe in a soapcalc that calls for 130gr NaOH. That amount is for a 100% pure NaOH. If you want to know how much is really needed for your 99% NaOH then this is the quotation:

Soda finally needed = (Soda 100% pure / soda 99% you have) * 130gr

So the above will be:

Soda finally needed = (100/99) * 130 => 1.01*130 => 131.3gr

Bare in mind also that after many uses and openings of the NaOH's package, it will absorb moisture and eventually by the last doses of NaOH in the package, it might be even less than 99% pure. Susie has an interesting way of compensating this purity loss, and might chime in soon describing the way.

Nikos

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Many online calculators assume a purity of less than 100% anyway, so from a safety point of view it's not an issue.

But from what you say, if you used less lye than the recipe called for and THEN added more oil, you effectively reduced the lye amount even further.

Thanks Nikos for your detailed explanation. I will do the math and see what i come up with.
Craig, I think your explanation makes a lot of sense. However, I used a lot of hard fats in this recipe so the soap came out nicely in the long run. Does that mean that I superfatted at 15 % ? Thanks for the input.

Allane

I've not worked out the exact numbers, but it is a higher SF than you would normally go for that much is certain. If you originally aimed for 5% and added in more fat, that would make it close to 10% but not quite -

If you had 1000g of oils originally aimed at a 10% SF (100g), then adding 5% of 1000 in again makes it 1050g total with 150g unsaponified oils. So then we have (150/1050) * 100 to get our new SF amount = 14.29%

Then we would have to factor in the lower lye purity to get the actual number. But that would be overkill as the calc is not so spot on with the numbers that we can really use them to get to that level of detail

Then the fact that your lye was 99 and not 100% pure

"...Many online calculators assume a purity of less than 100% anyway..."

Actually every calc I've looked at (not an exhaustive search, but around a dozen) assumes 100% purity for NaOH and most of them are also 100% purity for KOH (if they do KOH calculations, that is).

But honestly, the NaOH that the manufacturer makes and the NaOH that the soaper actually uses are two different things. It is so very unlikely that NaOH stays at 99% purity under normal storage conditions. If your soap feels too superfatted, I would suspect your lye is far less pure than you think due to reaction with moisture and CO2 naturally in the air. Even storage in a tightly closed bag or container is not good enough, since NaOH degrades so easily.

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Ah, sorry - I meant that there is always a built in superfat above that which we select

Oh, now I get your point. Yes, that makes sense, Gent!

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