Basic Chemical Additives

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Feb 25, 2017
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Hi everyone! I've been making soap for a couple of years and currently live in North Texas. We have crazy hard water. There is a chemical which is added to soap that reduces the film left on your skin after using soap in the shower. Does anyone know what it is? I haven't decided if I'm going to use it in a batch or not but I used to know what it was and not being able to remember is driving me nuts. Thank you for your input :D
Cirtic acid, sodium citrate, and edta.

Cirtic acid you must adjust your lye amount, because some gets used by the CA. I have never messed with this because of this reason.

Edta, I haven't used. I think, may be wrong, but think it needs a particular calculation which was more than I wanted. I could be wrong. I will say soaps I've swapped with edta, I think, are awesome quality wrt lack of soap scum.

I use sodium citrate. Easy to work with. Add 2%ppo.
So a 16 oz batch, I would use .32 oz SC. I predissolve it in my water with sugar @ 1TBS ppo and silk, if I choose to use it. After dissolved, I then add my lye. I bought a large supply fromm eBay. It's going on, oh, maybe 2 yrs now! I still have a ton left!

Here is where I get it

Just checked out ebay, and there's another seller I didn't see back then selling it for less per pound I believe. Just search ebay and you can get a good deal, if your interested.
I use citric acid just because I can get it in bulk at the local store.
Once you start doing the math it's not difficult.
Citric goes into the water before anything else ( like sugar) . The reaction with lye and citric is exothermic ( makes it hot) so go slowly when adding the lye to the water.
I typically add 2% by weight of oils to my soap.

If I remember correctly off the top of my head the math is : weight of oils times 0.02 times 0.624 equals the weight of sodium hydroxide (lye) needed to get to neutral.
So if I add 10 grams of citric acid to the water I need to add 6.2 grams of lye to the solution so I do not change the superfat of the recipe.

Clear as mud, right?
I have very hard water, too, and I use tetrasodium EDTA. Don't confuse it with disodium EDTA, though- tetrasodium EDTA is the type that you want for soap. I buy it in crystal/powdered form and make a proper 39% solution of it, which I store in a 12-oz bottle. I do that because it's much easier for me to work with it in solution form. The reason for the 39% is because that's the strongest concentration you can make out of EDTA without it precipitating out of the solution.

The cool thing with EDTA is that not only does it cut down on the scum, it also helps to prevent DOS.

As with citric acid, there is a little math involved in order to make sure I get enough of the actual EDTA from the diluted solution into the soap. Thankfully, the math is super short and easy. If I can do it, trust me- anyone can. lol

The amount of EDTA I like to use in my soap is .5% as per the weight of my entire batch, including the weight of the additives such as sugar, colorants, FO, etc...

After I've calculated the total weight of my batch (in grams, not ounces- very important), I do this simple 2-part equation:

1) Total batch weight in grams x .5% = how many grams of powdered EDTA is required for my batch (I write that figure down)
2) The gram amount of powdered EDTA required that I just wrote down x 2.56 = how much of the 39% solution to weigh out for my batch (in grams, not ounces)

That's it. Easy peasy. The solution can be added either to the oils or to the lye solution or to your soap batter, it really doesn't matter just as long as you remember add it. lol

IrishLass :)
"...The reason for the 39% is because that's the strongest concentration you can make out of EDTA without it precipitating out of the solution...."

I came across some info recently from Sigma Aldrich who makes EDTA. The tech sheet I looked at suggests tetrasodium EDTA can be made into a solution with water at up to a 55% concentration (55 grams EDTA plus enough water to make a total of 100 grams of solution). I have yet to verify this for myself, but it might be worth checking into. If it works, I might do a 50% solution -- that would make the math simpler and reduce the amount of water supplied by the EDTA solution by a bit.

I am pretty sure the 39% solution concentration is a number that relates more to how EDTA is used in industry. It turns out 1 gram of 39% EDTA solution will chelate 1 millimoles of metal ions. When you are frequently adjusting the chelation dosage in an industrial process, using an easy-to-remember number like this makes the calculations simpler and reduces the chance of error.

I realize this is a little off topic for the OP, but Irish Lass's post (above) triggered my memory. I wanted to make sure I got this info shared, before I forgot!
Thanks, DeeAnna! That's interesting! The next time I need to mix up another batch of solution, I'll try a 50% solution and see how it goes, and report back!

IrishLass :)
I will do the same as well. Like I said, it's a tidbit I stumbled across the other day when doing some reading. I have not yet tried it to see if what works in industry also works in my kitchen. :)
I very recently made up a batch of 39% EDTA solution, which I expect will last me at least 3 months or so. But if a 50% solution is possible, that would be great, because it certainly would make the math a bit simpler.

Ensmartened, I like tetrasodium EDTA for both properties: reducing soap scum and helping to prevent DOS. I use it in combination with ROE as per Dr. Kevin Dunn's findings that they work well together. (see page three in this article)
Yep, I'm here to tell ya ... it really does work.

The EDTA powder takes awhile completely dissolve at a 50% concentration. To help it dissolve, I warmed the water slightly (warm to the touch -- maybe 95 F, 35 C) as well as stirred for minute or so. I do not think the warmth is strictly necessary, however. The solution remained cloudy for several minutes after all the particles were obviously dissolved, but the cloudiness looked more like fine gas bubbles rather than solid particles.

After about 5 minutes, the solution is now clear, and I'm pleased with the outcome. I will check the mixture tomorrow and will report back if there is any change ... but I bet it will be just fine.
Thank you so much for all of this information! I'm out of state just now but I'm going to implement this with my next batch and see how it goes. :D
Thanks for this tutorial on Chemical Additives. Question please: Apart from preventing DOS and reducing soap scum, will the use of sodium citrate extend shelf life of soap?

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