Tetrasodium EDTA
Binds hard-water minerals, for less soap scum. Sold to hold off rancidity and orange spots.
Opens the calculator’s starter recipe, 1000 g of oils, with this additive at the dose it fills in, ready to change.
What it is
Tetrasodium EDTA is the tetrasodium salt of EDTA, a chelating agent sold as a powder in grades of different bulk density. Dow’s data for it in bar soap name what the metal ions it binds would otherwise cause: softening, brown spots, rancidity, cracking and discolouration.
How much
- 0.1–0.2 % of the batch filled in Dow primary source
- 0.05–0.25 % of the batch Classic Bells supplier or guide
- 0.1 % of the oils in a controlled test Dunn, “The Dreaded Orange Spot” primary source
- up to 0.56 % of the batch in rinse-off products, the highest reported use: not a recommendation CIR primary source
The calculator fills in 0.1 % of the batch: 1.4 g for the 1000 g of oils in its starter recipe.
When and how
- Usually: in the water, before the lye.
- Weigh it dry and dissolve it in the recipe’s own water: no extra water.
Dunn, Scientific Soapmaking primary source, Classic Bells supplier or guide
What it does to the recipe
- It changes neither the lye nor the water: it is only weight in the bar.
Dow primary source, Classic Bells supplier or guide
Worth knowing
- In Dunn’s test, at 0.1 % of the oils, it held off rancidity longest: beyond 300 hours. Dunn, “The Dreaded Orange Spot” primary source
Spoons and drops
- 1 tsp ≈ 3.7 g (2.96–4.44 g)
- 1 tbsp ≈ 11.1 g (8.87–13.3 g)
- 1 cup ≈ 177 g (142–213 g)
Nouryon primary source
INCI name
Tetrasodium EDTA
- CAS number
- 64-02-8
- EC number
- 200-573-9
Recipes that use it
Guides that discuss it
Sources
The Dow Chemical Company, VERSENE Chelating Agents (2007): in bar soap 0.1–0.2 %, where it "Helps prevent softening, brown-spotting, rancidity, cracking and discoloration due to metal ions"; disodium EDTA is "for use in products at neutral pH".
Classic Bells, "EDTA": 0.05–0.25 % for rancidity; "Do not adjust your lye weight for EDTA"; disodium EDTA stirred into the lye becomes tetrasodium EDTA with "a small excess of NaOH", 22 g per 100 g (untested by the author).
Kevin M. Dunn, Scientific Soapmaking (Clavicula Press, 2010): "666 g of sodium hydroxide to react with 1000 g of acetic acid" (p. 165); vinegar is about 5 % acetic acid (p. 175); 10 g of NaOH neutralise 16.01 g of citric acid (pp. 354–355); "The most potent preservative was edta ... when added to the lye at a rate of as little as 0.3 ppt" (p. 285).
Kevin M. Dunn, "The Dreaded Orange Spot", The Handcrafted Soapmaker (Winter 2005/06): additives at 0.1 % of the oil weight in olive-oil soap held at 60 °C. Rosemary extract and EDTA "lengthened the induction period beyond 300 hours", BHT to 150; grapefruit seed extract, vitamin C, vitamin E and sodium citrate were "virtually identical" to plain olive-oil soap; BHT with sodium citrate did best, and "ROE + Sodium Citrate actually performed worse than ROE alone".
Cosmetic Ingredient Review, EDTA and its salts (2002): tetrasodium EDTA up to 0.56 % and disodium EDTA up to 0.25 % in bath soaps and detergents.
The highest concentration reported to CIR in industry surveys: what has been used, not a recommendation.
Nouryon, Dissolvine product guide (2021), p. 7: tetrasodium EDTA powder, poured bulk density 600, 750 and 900 kg/m³ by grade.