Lye precipitation?

[bathgeek]

Hi all,

For those of you who use masterbatched lye solutions, do you get lye precipitating to the bottom after a while? I always have to shake up my storage containers before use. I always wait for my lye solution to cool and I ensure it’s 50% before I pour it into the jugs and store it, but i always get precipitate. New to master batching. Is there something I’m doing wrong, or is this just the nature of the beast?

 

[jcandleattic]

Honestly, I don't know. My masterbatch container is a giant cleaned out liquid laundry jug, and I always gently shake my container (with the lid securely on, and my eye protection in place) before each use. I think as long as the participate dissolves back in, it's fine, otherwise you could strain it in a small strainer to get any lumps/particles to not get in your soap.

 

[DeeAnna]

Yes, there can be a precipitate. Let's say you have weighed the water and sodium hydroxide (NaOH) with reasonable care and you verify the sodium hydroxide is fully dissolved when you make the masterbatch solution and you keep the solution tightly capped to prevent any water evaporation. Keep in mind, these are all reasonable things that are easy to do by a reasonably careful person.

If so, then this precipitate is sodium carbonate (Na2CO3, washing soda, soda ash), not NaOH. I'm as reasonably sure of that as I can be without a chemistry lab to do the testing and without personally watching you make your masterbatch solution.

Remember the most common impurities in NaOH, even coming right out of the manufacturer's door, are water and soda ash. When you make a nearly saturated masterbatch solution of sodium hydroxide in water, the NaOH (a very strong alkali) will be a lot more soluble than the sodium carbonate, a weak salt of NaOH.

The same thing happens when people make the lye solution for solsiefe (sp?) soap -- you dissolve table salt (another salt of NaOH) in plain water to get a clear solution. Then you add the NaOH and the mixture turns milky. The "milk" is the salt that precipitates out of solution to form tiny salt crystals. If you left this lye mixture to sit for a time, the salt would eventually settle in a layer on the bottom of the container.

 

[earlene]

I store my mb lye in opaque containers (Essential Depot containers that the lye came in originally) so I do look before shaking, but they are not clear enough to see if there is really any particulate matter on the bottom.

I do know, that it does get thicker as the bottle becomes less full, which I conclude is the result of more air and less solution, allowing for more oxygen to interact with the chemicals in solution. But not thick enough to form visible particulate matter.

I always shake before use to ensure the solution is well mixed, but that is more a lifelong habit of dealing with solutions, than because I think it may come out of solution. I don't think it really can come out of solution when it is a 50:50 mix, so long as no evaporation has occurred. IrishLass suggests weighing before and after and any loss of total weight is due to evaporation, and therefore you need to add back in the missing weight in distilled water. Here is IrishLass's post on how she does the masterbatch taking water evaporation into account:
https://www.soapmakingforum.com/threads/lye-solution-master-batch.18098/#post-168524

 

[cmzaha]

Yes I get a little in the bottom of my container. I see it once my jug is empty, not so sure it is lye, but never the less it has never affected my soap, at least not noticeably.

 

[IrishLass]

Here is IrishLass's post on how she does the masterbatch taking water evaporation into account:
https://www.soapmakingforum.com/threads/lye-solution-master-batch.18098/#post-168524

It looks like that one only shows how to use the solution in one's soap (instead of accounting for evaporation while making the solution itself). I think this is the link you are looking for: https://www.soapmakingforum.com/threads/storing-lye-water.30081/#post-282644

Basically, it's as Earlene says in her post- when making my 50/50 solution, I take a before-and-after account of the weight of everything, i.e. lye, water, and my mixing container and cover. That's because evaporation occurs as I am mixing the solution (usually 6 grams worth or so of water vapor goes missing into the air for me during the exothermic reaction, sometimes a little more, depending). My after weight tells me how much water evaporated/how much water I need to add back into my solution to bring it back up to 50/50 solution, which I do before I transfer it into its storage jug and cover it.

I also take a before-and-after account of the weight of my final storage jug and its cover- I weigh the covered jug empty, and then I weigh it once it's filled up with my solution, and I write both of those weights down on a piece of masking tape which gets taped to the jug.

When I go to make a batch of soap with my stored master-batch lye, I weigh the filled jug to make sure it agrees with the weight previously written down on the masking tape (it always does, by the way). Then, after I've poured out however much solution I need for my batch, I weigh the jug again and write the new weight on a new piece of masking tape and stick it to the jug (after scratching out the old weight)......so that the next time I go to make a batch, I can make sure that my solution is still 50/50 (which it always is, by the way.....no matter how long I go between making batches. Even if it's been over a year since my last batch, the weights have always matched up.


IrishLass

 

[bathgeek]

Good to know it’s not just me! I was always a little concerned, but my soap wasn’t zapping and it didn’t seem like the superfat was excessive.

Btw, DeeAnna, I am absolutely in awe of you. <3 Thank you did the clear explanation.

I do exactly what you described, IrishLass. (I learned how to masterbatch from that post. ^_^) That’s one of the reasons it confused me, because it wasn’t an evaporation thing, weights were matching up.

 

[earlene]

It looks like that one only shows how to use the solution in one's soap (instead of accounting for evaporation while making the solution itself). I think this is the link you are looking for: https://www.soapmakingforum.com/threads/storing-lye-water.30081/#post-282644

IrishLass

You are correct, IL, I don't know how I managed to copy & paste the wrong link. Thank you for catching that!

 

[cmzaha]

I really like what IL does but I am not about to handle my gallon of lye in order to weight it on my scale. My hands just are not reliable enough and I feel the more I handle it the more chance of an accident. I just figure it the lye precipitates out because water has evaporated they should work out in the end. Nope not very scientific but I do not have any problems with my soaps except when I make an outright error, which I recently did. Only ended up with over 50% superfat

 

[jcandleattic]

I just figure it the lye precipitates out because water has evaporated they should work out in the end.

I feel the only concern (which is not very concerning unless you are totally a newbie) is a higher water discount, and your batter may move faster. So eh...

 

[DeeAnna]

If Irish Lass is losing about 6 grams of water when making her masterbatch. Assuming she makes a 1 liter amount of solution, that 6 gram loss is less than 0.5% of the total weight. If a person doesn't add back the evaporated water, that loss essentially makes the NaOH solution a little more concentrated, but only by a very small amount.

It is always good to work as accurately as possible, but sometimes doing a good job is as much about consistency as accuracy. IL compensates for water loss. Carolyn doesn't. But they both make good soap because (a) the error involved is small and (b) each one deals with it in a consistent way.

Another tip to reduce water loss and also to minimize irritating NaOH fumes from escaping into the room air -- keep the container of hot lye solution lightly covered at all times. I cover the container with a piece of paper towel and discard the paper after the solution cools. If you mix your lye solution in a container with a cap or lid, you could lightly set the cap on the container. Don't make a tight seal to prevent pressure from building up.

 

[cmzaha]

I do cover mine container with a 12" x 12" sheet of Grease Resistant sandwich wrap. That I did forget to mention

 

[mx5inpenn]

I used to weigh my masterbatched lye once it cooled. It was always 5 to 10 grams short, so that is the amount of evaporate during mixing. After at least 10 times getting that range, I just started adding 10 extra grams of water at the start. If there's an extra couple grams of water at the end, the difference in a batch of soap is negligible.

 

[bathgeek]

I used to weigh my masterbatched lye once it cooled. It was always 5 to 10 grams short, so that is the amount of evaporate during mixing. After at least 10 times getting that range, I just started adding 10 extra grams of water at the start. If there's an extra couple grams of water at the end, the difference in a batch of soap is negligible.

I do that too. ^_^ My method is:

1. Weigh the empty mixing container (now I have a standard one and the empty weight is written on it with marker.)
2. pour some water (roughly what I expect it to be at the end)
3. Weigh lye container with lye
4. Pour lye into water
5. Weigh empty lye container and calculate amount of lye in water
6. Repeat steps 3-5 until I have the amount of lye I want
7. Calculate what weight of lye + water + empty container should be
8. Stir until lye is dissolved and leave alone to cool
9. Weigh mixing container and lye mixture, then add water to get to the final desired weight.
10. Once satisfied solution is 50%, pour into storage container.

 

[Soapmaker123]

The lye batch that I prepare is dense, but not saturated. Even so, after sitting at rest, the lye density at the bottom of the tank will exceed the lye density at the top of the tank: it stratifies.

So, I stir and stir the lye tank just seconds before I release a measured amount of lye through the valve.

Bad things happen to soap when the lye solution stratifies.

But I've never gotten lye precipitate. Perhaps your lye density exceeds saturation?

 

[bathgeek]

I doubt my lye density exceeds saturation, since it's absolutely clear when I pour it out of the mixing beaker into the storage jug. That's why I asked about precipitate. I like DeeAnna's explanation, which makes sense to me.

 

[Soapmaker123]

Maybe, at rest and with time, the solution stratifies to the point that the bottom layer reaches saturation? See if vigorous stirring drives the the precipitate back into solution as the bottom layer mixes back in with the lighter layers.

 

[bathgeek]

I use the lye solution almost daily though. That seems pretty fast!

And no, it doesn’t seem to dissolve again as far as I can tell.

 

[JENNIFER L GREENWOOD]

Yes, there can be a precipitate. Let's say you have weighed the water and sodium hydroxide (NaOH) with reasonable care and you verify the sodium hydroxide is fully dissolved when you make the masterbatch solution and you keep the solution tightly capped to prevent any water evaporation. Keep in mind, these are all reasonable things that are easy to do by a reasonably careful person.

If so, then this precipitate is sodium carbonate (Na2CO3, washing soda, soda ash), not NaOH. I'm as reasonably sure of that as I can be without a chemistry lab to do the testing and without personally watching you make your masterbatch solution.

Remember the most common impurities in NaOH, even coming right out of the manufacturer's door, are water and soda ash. When you make a nearly saturated masterbatch solution of sodium hydroxide in water, the NaOH (a very strong alkali) will be a lot more soluble than the sodium carbonate, a weak salt of NaOH.

The same thing happens when people make the lye solution for solsiefe (sp?) soap -- you dissolve table salt (another salt of NaOH) in plain water to get a clear solution. Then you add the NaOH and the mixture turns milky. The "milk" is the salt that precipitates out of solution to form tiny salt crystals. If you left this lye mixture to sit for a time, the salt would eventually settle in a layer on the bottom of the container.

you sound so smart-- this is close to my question-the subject at least.... I made lye water and went for a hike- I was gone longer than intended and its room temp- how do I warm lye up?

 

[shunt2011]

you sound so smart-- this is close to my question-the subject at least.... I made lye water and went for a hike- I was gone longer than intended and its room temp- how do I warm lye up?

You really don't need to warm up your lye mixture to use it. I soap with room temp lye all the time. However, if you want to warm it a bit you can fill your sink with hot water and place your lye container in the water. It will take any chill off.