Lye Master Batch

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Fireside

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I master-batched a 50% lye solution (20 oz lye added to 20 oz water) and the lye does not appear to have dissolved fully. There is some just sitting at the bottom of the container. Does anyone know why this is? Never having been mistaken for a patient person, I wonder if I added the lye to the water too quickly. If I make sure to stir the solution thoroughly before adding it to a recipe, will it be safe? When I add the required amount of water to the 50% solution to make the lye solution appropriate for my recipe, whatever lye is in suspension dissolves, giving me a clear liquid to add to the oils. Can I use it like this or should I just get rid of it? I haven't seen anyone else mention their 50% solution not dissolving fully. Thanks!
 
It could be that you didn't stir it well enough to completely dissolve, or that you stored it below 62F, which would make the lye precipitate out.

Most likely you lost some water to evaporation from the heat, leaving less than 50% water, which would also cause the lye to precipitate out. If you weight the entire container, and subtract the container weight, you should have a total of 40 oz. If it is less than that, you will want to add enough distilled water to reach 40oz.

If you have 40oz of water, try stirring it again and see if it dissolves. If not, you can try heating it gently, or adding more water, which will also cause it to heat up again, and will help the remaining lye dissolve. If all else fails, strain out the lye that didn't dissolve. You can still use the solution but will have to figure out the strength based on the amount of lye you removed, and the total weight of the solution.
 
It probably wasn't exactly 50/50. You should put slightly more in. It won't be perfect but it will work as long as you don't add too much. Say, another 0.1 ounces.
 
You don't clearly explain what you're seeing in the bottom of the container. Is it flakes or pellets that look like the original form of your dry NaOH? Is it a clear solid layer? Is it a fine white powder?

If it's the first two options, it's likely one of two things -- either you don't have enough water to properly dissolve the NaOH OR the NaOH solution is too cold for all the NaOH to dissolve properly in the first place or for it to remain in solution as time passes.

If the last one, it's likely sodium carbonate that's settled to the bottom. Sodium carbonate is a normal impurity in NaOH that will settle out if you let the lye solution sit for a time. Stir it up, measure the solution as normal, and make your soap.
 
Thanks for advising, you three. I was beginning to think nobody cared about my problem (I'm a little insecure that way).

I had a 50/50 mix, within less than 0.05 ounces (my scale is accurate to .05 ounce). I added water as it evaporated to keep a total of 40 ounces of solution. I did make a batch of soap with the solution right after I made it and cooled it and the soap looks normal. This morning (four days later) I weighed what's left and it's about 4.5 ounces less than it should be so maybe more water than I thought has evaporated. If I replace that water and gently heat the solution, maybe the rest of the lye will dissolve (unless it's not undissolved lye: what I see at the bottom of the container does look like a fine white powder). I'll try it. If anyone thinks I shouldn't use this new solution in soap, please let me know and I will use it to clear some slow-draining drains instead. Thanks!
 
Update: I decided to just clear my drains with the stuff. Here's why: I added the extra water, watched it heat up, stirred, hoped the particles would go away but they wouldn't, and then had a minor mishap that I won't go into that caused some loss of solution, so I just got rid of it. The white stuff, whether it was undissolved lye or sodium carbonate, was bugging me and I wanted to be done with it. I will try again and be more patient to be sure the lye has time to dissolve before I add more. Blah. Thanks for trying to help.
 
Update: I made another master batch this morning and this time I added the lye much more slowly: added a little, stirred till it dissolved, added a little, stirred till it dissolved, and so on. That seemed to work. It's still cooling (it's at about 135 degrees now) and I've added water to compensate for evaporation. Some white stuff is floating on top, which I assume is the sodium carbonate because someone somewhere (it might have been DeeAnna in another lye-related thread) wrote that once the lye has dissolved, it can't "undissolve." I hope that's what it is.

Happy Easter!
 
Update: I made another master batch this morning and this time I added the lye much more slowly: added a little, stirred till it dissolved, added a little, stirred till it dissolved, and so on. That seemed to work. It's still cooling (it's at about 135 degrees now) and I've added water to compensate for evaporation. Some white stuff is floating on top, which I assume is the sodium carbonate because someone somewhere (it might have been DeeAnna in another lye-related thread) wrote that once the lye has dissolved, it can't "undissolve." I hope that's what it is.

Happy Easter!
Sounds like it’s going to be a good batch. If you are starting to see ash (lye lint) on top, I’d cover it so no more lye is converted to soda ash.
 
"...(it might have been DeeAnna in another lye-related thread) wrote that once the lye has dissolved, it can't "undissolve."..."

I think I remember that discussion -- it was in a thread talking about how the OP thought there were supposedly solid particles of NaOH soap in the OP's soap. I think in the posts that followed, it sounded like the OP had gotten their lye solution made properly so all of the NaOH was dissolved when they made the soap. I said something to the effect that once NaOH is dissolved in water, it doesn't magically un-dissolve.

That said, there are times when NaOH in a water mixture can precipitate (become solid again). But there has to be a good reason for this to happen.

As I mentioned earlier in this thread, NaOH can precipitate back into solid form or not fully dissolve in the first place if (a) there is not "...enough water to properly dissolve the NaOH OR (b) the NaOH solution is too cold for all the NaOH ... to remain in solution as time passes...."

To prevent problem (a) from happening, the concentration of the NaOH solution should be no higher than 50% (1:1 water:lye ratio).

To prevent problem (b), I recommend keeping 33% to 50% lye solution at or above 65 deg F / 22 deg C to minimize the chance the NaOH will precipitate out of solution due to being too cold.
 
That said, there are times when NaOH in a water mixture can precipitate (become solid again). But there has to be a good reason for this to happen.
If this were to happen due to storing at too low a temperature, do you know if gently heating the solution to above 65F would reincorporate the solid NaOH?
 
@Fireside -- Yes, theoretically heating the solution should re-dissolve the NaOH, but I'm not sure I'd want to try it for a number of reasons --

In my experience the NaOH precipitated as a solid sheet of chemical. This will re-dissolve veerrrry slowly with heat alone due to lack of surface area. Also there's a safety issue if you try to break up the sheet of solid NaOH in a bath of concentrated NaOH solution -- there's a very high probability of spatters and spills and the risk of injury is high. Also there's a chance of explosive boiling if there is any liquid trapped beneath the solid sheet of chemical and that liquid is heated to the boiling point of the solution.

IMO, it's better to add water to re-dissolve the NaOH. Keep track of the weight of water added. Measure the total weight after the NaOH is back in solution. This information along with the starting concentration will let you recalculate the ending concentration.

edited: clarified meaning
 
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