soap making

Testing EDTA in Soap

I made a small and casual experimenting with this additive and thought you might be interested in the results.

It all started because the lye calculator that I use ( displayed suggested amounts of it for my recipes, which made me look it up.  It turns out it is a “chelating agent” which means it binds up metal particles.  More detailed explanation here.  Learning the word chelator, chelating, etc, made it easy to understand some episodes of House whenever they had a patient with metal poisoning.  But that is besides the point.

What does it do?

  1. Tetrasodium EDTA reduces DOS and
  2. it also reduces sticky soap scum in hard water areas (given that hard water may have some trace metals in it, among minerals as well)  more information on that here.

My experiment explored the latter, since thank God I have never had DOS on my soap  (knock on wood!).  However, that can be explained because my recipes have a high content of saturated fats (tallow, coconut oil, shea butter) and DOS is most common in non saturated oils (the ones that stay liquid, olive oil, rice bran oil, etc) since they oxidize faster.

The experiment

It consisted basically of using two soaps to wash my hands twice a day.  (I wash my hands like  100 times a day, but only twice at the sink by my bedroom.)  I did that for about a week the first time and the results were visibly evident:  (the dark brown soap did not have Tetrasodium EDTA and the pinkish one did.)  They were made around the same time, and had cured for about two months.

The Second Experiment

I decided it was not fair to the brown soap to be compared with a lighter colored soap, so I looked for a similar tone soap in my curing rack (where soaps stay until I need them).  The closest one was the peach soap.  Which had cured (sat on the rack) for about 6 months.  After 10 days, this is what I had:

The results were less visibly obvious.  So I had to get tactile.  I could feel the soap scum was thicker on the peach soap side, vs the pinkish soap.

I then rinsed the soap dish in water to see which side would get cleaner from plain contact with water without any scrubbing.  And pinkish soap won again, the side where it had rested was smoother and has less residue than the side with the peach soap.  So my deduction is that cleaning the shower would be easier if I add EDTA to my soaps, since I live in a hard water area and do not have a water softener.

If you want to watch the experiment in video, click here.

What about DOS?

Since I do not get DOS with my soaps (and I have some toddler soaps -they are 2 year old), I looked for an experiment done for that purpose.  It is a bit scientificky, but an actual easy read.  You can read it here.  And here is a shorter version.

Basically, he proved it works to reduce DOS, and suggests it works even better in combination with ROE (Rosemary Oleoresin, which I bought at Wholesale Supplies but have not tried it)

How to use it, where to get it

If you want to try it yourself. these are the two places where I have bought it:

Lotion Crafter

Make Your Own (Aff link)

Usage rate

EDTA is also use to help the preservative (if used in lotions, in which case you use Disodium EDTA).  For that, the usage rate is 0.10%.

In Kevin Dunn experiments, he used it at a 0.10% rate based on the oil weight.

In a soap making forum, I found the suggested usage rate went up to 0.50% of the total batch.  Based on the experience of other soap makers.

The lye calculator I use already includes the suggested amount, so I follow that.  Here is a sample recipe where you can see it.


Just a few days before this blog going live, I learned that there is an alternative that is better for the environment, as there concerns about it.

This came up in a forum thread which can be read here.

The alternative is GLDA and it can be purchased here.

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