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Making Lye Solutions – Cold Water vs Room Temperature Water

Okay, here’s a little something that might interest the more seasoned soapers out there. I’m not sure if it’s something you already know, but here are my experiences anyway.

I’ve come to the conclusion that the temperature of the water with which you make your lye (sodium hydroxide, or NaOH) solution influences the outcome of whether or not your soap ends up with lots of ash on the surface.

My observations: ice water leads up to higher occurrence of soaper’s ash, while room temperature water leads to much less ash, if at all.

You see, when you add NaOH to water, the reaction is exothermic, meaning it produces heat. In fact, it gets REALLY hot, hitting close to 90C. It takes some time for me to cool it down in a water bath to get it to the correct soapmaking temperature, which is between 34C to 42C.

So there were a couple of occasions where I decided to ‘cheat’ by adding ice cubes directly to my lye-making water so the solution, thinking that I could cut down my waiting time for the lye to cool.

Well, cool faster it did, and my soaps turns out fine. But I noticed that for these batches, a fine layer of ash completely covered my soap. At first I put it down to just air getting into the mold while it was covered with cloth. Then I decided to check if it was the temperature of the water to which I added my NaOH by making two separate batches of soap where the only difference was the temperature of my water for the lye solution.

One batch had water that was at room temperature, about 24C. The other batch had ice water which brought its temperature down to 11C. I made my soap as normal then loosely covered the raw soap with clean dishcloths.

Result: the batch with room temperature water had only a minimal amount of ash resting on the crests of the soap swirls. The batch with the ice water had a fine, even layer of ash that completely covered the soap, even in the valleys of the soap swirls. It looked like powdery snow actually.

Now you know what to do to achieve the desired effect for your soap. 🙂

(Alas, I forgot to take photos. DOH! #-o )

9 thoughts on “Making Lye Solutions – Cold Water vs Room Temperature Water

  1. Well, looks like the keeping a lid on the mold is the best way to avoid ash! 😀

    Mike: Yup, I came to the same realisation when I first started out as well. Another thing I noticed with my soap was that I could never really leave them unwrapped past 4 weeks, because most of them started to absorb moisture instead of lose it, and the oils tended to spoil despite me including rosemary oleoresin.

  2. I’ve not been making soaps for quite a while, Michelle. After thinking about my process. My soaps end up without much ash because I put a lid on it! Any lid will do, even a cardboard. I use polystyrene to cover it. It doesn’t have to be air tight just enough to keep the heat in. Uncover only after the soap is totally cool down. That should make a big difference!

  3. Hi Michelle,
    Correct, we do not heat the oils, everything done at room temperature. Luckily all of our oils are liquid at room temperature which is usually around 30 C.

    Our block moulds (imported from the USA) are made from thick PVC (nearly 2 cm thick) so they are self-insulated. On the top I place a few layers of corrugated cardboard to help keep the heat in.

    Thing to keep in mind is that most soap making books are not written for tropical climates, so in these cold countries there is a pre-occupation with heating and insulation. In our Malaysian climate this is not really necessary.

  4. We mix our NaOH the day before, so when mixing soap batches everything is done at room temperature (usually around 30 C). We actually record the temperature for each batch. Generally we don’t have issues with ash, however sometimes it appears for some reason even though all of our processes are standard. My thinking is that overnight minimum room temperature may be an influence.

    1. Hi Mike, thanks for sharing. You mean you don’t warm up your oils before mixing with lye? Ah, that sounds so much simpler. Unfortunately because I use cocoa butter in most of my formulations, I have no choice but to spend some time to get the oils warmer than 34C so the cocoa butter can melt. Do you insulate your molds? That’s one thing I’ve not tried yet. I see most US soapers have molds that have proper fitted lids to keep the heat in, and their soaps look fantastic without any ash.

  5. Oh! I think if you’ve stirred it to medium to heavy trace it shouldn’t be too ashy. Having said that, you can’t really stir it when it’s too heavy, doesn’t it? I normally use the hand-held blender and pause it for 10 – 15 times until I see the colour changes and hand stir it until light trace. I wonder if those ashes are from air bubble by using hand blender?

    1. That’s interesting, you blend first, and then stir by hand? I should try that! Thanks for the tip. I use the blender all the way, but it does mean that it ends up with some air bubbles trapped in the soap bar sometimes. Not so pretty. :( I see that your soaps are practically free from air bubbles, are they? Maybe stirring by hand at the last stretch is the key!

      But I don’t think the surface ash would have been caused mainly by the hand blender, cuz it only affects the surface of the soap, not the air bubbles inside. Maybe it’s a timing issue. Perhaps because you take slightly longer to stir by hand, saponification is more complete by the time you allow the soap to set in the mold, as opposed to the super-fast hand-held blender method, where the lye hasn’t completely reacted with the oils yet? So in the quick blend method, more lye on the surface is allowed to react with air and turns into ash?

      I’m pulling this out of my @$$ of course. Does it make sense to you? :p

  6. That’s interesting. Although I have a difference experience. If the lye and oil are both well stirred, I had very little ash. Compare to oil that is only been stirred to light trace.

    1. Ah, okay, that’s interesting to note. I’ll keep that in mind. So far I prefer to have my soap poured at medium to heavy trace so I get either a chunky effect or at least mild swirls and mounds for an interesting texture. On to experiment with light traces soon. ;)

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