Lye water will not clear - stays white ?????????

[Karyn]

Hi all and TIA for any help/thoughts.
My recipe calls for 20% saltwater solution. When I mix lye I use 1142 grams of the saltwater solution and 635 grams of lye crystals. (Total oils in recipe is 4571 grams, but I don't think that matters for my issue.)
The lye water stays white and doesn't ever seem to clear. I work fairly hot, but even after sitting for an hour or more it stays an opaque milk white that is fairly thick if I've waited for a while. I run it through a fine strainer when pouring into the oils and everything seems to be ok...but I never have clear lye water.
Does it matter?
Thanks!

 

[Obsidian]

Its the salt, it will make your lye solution milky. Its perfectly fine.

 

[Karyn]

Thank you!!

 

[tildy]

Just let it cool down. You can make it a day or two ahead and have it clear. The hazy will clear up in a few hours.

 

[DeeAnna]

No, a lye mixture made with a 20% salt solution will never be clear. It will always be milky because salt (sodium chloride) isn't very soluble after you add the NaOH. Most of the salt in the (formerly clear) salt-and-plain-water solution will turn back into super-fine salt crystals after you add the NaOH. That is why the mixture is cloudy, and this is a normal thing to expect.

If you let a salt-NaOH solution sit for awhile, the fine crystals will settle out. You should stir the salt back into the liquid before you use the mixture. Don't discard the solids -- you want those superfine salt crystals to be in your soap, because this is the point of making soap with this particular method.

 

[DeeAnna]

Threads closely related to this thread --
https://www.soapmakingforum.com/threads/crystals-precipitating-from-lyewater-solution.79956/https://www.soapmakingforum.com/threads/dissolving-salt.60845/https://www.soapmakingforum.com/threads/salt-to-replace-sl.74246/
And a thread that's not as directly related to this one, but still helpful --
https://www.soapmakingforum.com/threads/lye-precipitation.69223/

 

[Nostalgicgranny]

I thought you need twice the amount of water in order for the lye to dissolve properly. Or does it not apply here???

 

[ResolvableOwl]

from https://www.oxy.com/ourbusinesses/chemicals/products/documents/causticsoda/caustic.pdf

At temperature 20°C/68°F, solubility (= not crossing the “solidifying curve”) is at concentrations at/anywhere below 52%. The higher the temperature, the higher the saturation concentration will be. Three parts NaOH per part of water around 70°C.

There is a temperature where the maximum solubility is 33% (1 part NaOH in 2 parts water), that's at around 8°C/46°F.

ETA: Drifting off-topic rapidly, a stunning detail of this phase diagram is the minimum around 45%/6°C: It suggests that preparing a solution there, and diluting it with water (moving left in the diagram) will cause NaOH to precipitate .

 

[earlene]

I thought you need twice the amount of water in order for the lye to dissolve properly. Or does it not apply here???

Properly?



1:1 ratio of NaOH to water will completely dissolve to sodium hydroxide lye. It does heat up enough that some evaporation does occur, which is why I always keep a lid on it, so the vapor will drip back down into the solution. But I also weigh the finished solution and add back in the same amount of water that appears to be lost in escaped evaporation (during mixing, before the lid is securely placed.) This last part, I learned here at SMF - replacing the evaporated water.

Even with a thoroughly dissolved 1:1 solution, if stored at colder temperatures (as RO alludes to in the above post), some will precipitate out and form a solid crystalized disk at the bottom of the storage vessel, so storage temperature is important. Refer to the quoted text below for a 'too cold for 1:1 lye solution' storage range:

If a 50% NaOH solution becomes sufficiently cold enough -- somewhere between 50 F (10 C) and 60 F (15 C) -- then the solubility of the NaOH drops and it may indeed precipitate.

Incidentally, for the sake of clarity, a 1:1 ratio = 50% solution (aka 50% lye concentration).

Just as another point of clarification, not all lye is sodium hydroxide, so the type of lye used to make a solution will alter the amount of water required for complete dissolution. But I believe this discussion is about sodium hydroxide/NaOH/caustic soda.

 

[ResolvableOwl]

So, to clarify (pun intended) that brine-vs-lye topic once for all, let's have a peek into the literature:

Solubility of common salt decreases rapidly with increasing NaOH strength:

from Atherton Seidell: Solubilities of Inorganic and Organic Compounds (1919), p. 644

Right column: the last but one entry (500 g NaOH per litre of solution) corresponds to some 35% lye concentration, i. e. a bit lower than the 37% of ZNSC. (I've ignored the bicarbonate for now, though it's subject to similar effects.)
The 1 tbsp/L of salt of the original recipe doesn't sound like much, but it is actually pretty close to the solubility limit of NaCl in the final lye! Any attempt to increase NaCl concentration well beyond that, will end up with salt precipitation, hence a salt bar (with solid salt crystals), not a brine bar in the narrower sense (all salt dissolved at any time).

Bonus insight: The orthodox 1:1.7 ZNSC would not work with true sea water! Or at least you would have to use water from the Baltic or Black sea, not from oceans.