Red iron oxide
Red.
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
Red iron oxide is a pigment powder, made by LANXESS among others, that holds its colour at soap’s high pH.
LANXESS; EFSA primary source, Mad Micas supplier or guide
How much
- up to 0.5 tsp per pound of soap filled in Wholesale Supplies Plus supplier or guide
- 1 tsp per pound of oils Mad Micas supplier or guide
The calculator fills in 0.5 tsp per pound of soap: 6.6 g for the 1000 g of oils in its starter recipe.
When and how
- Usually: at light trace.
- Mix it first with a little of the recipe’s oil, about a teaspoon of powder to a tablespoon of oil, so it spreads without specks.
Wholesale Supplies Plus supplier or guide
What it does to the recipe
- It changes neither the lye nor the water: it is only weight in the bar.
Worth knowing
- Stirred in dry, it leaves specks: mix it with a little oil or water first. Wholesale Supplies Plus supplier or guide
- Too much colours the lather. Lovin Soap supplier or guide
Spoons and drops
- 1 tsp ≈ 4.19 g (2.96–5.42 g)
- 1 tbsp ≈ 12.6 g (8.87–16.3 g)
- 1 cup ≈ 201 g (142–260 g)
LANXESS; EFSA primary source
INCI name
CI 77491 (Colour Index number)
- CAS number
- 1309-37-1, 1317-61-9, 1345-27-3, 52357-70-7, 1345-25-1
- EC number
- 215-168-2, 215-277-5, 215-722-3, 257-870-1, 215-721-8
- US colour additive name
- Iron Oxides
Recipes that use it
Guides that discuss it
Sources
Wholesale Supplies Plus, soap colorants guide: titanium dioxide is "prized for its dense, white opacity", and "A single teaspoon is sufficient to lighten one pound of soap"; "half of this amount or even less for brown oxide and red oxide"; oxides "must be thoroughly mixed with oil before use"; micas offer "a spectrum of bright hues"; ultramarines have "potential to emit sulfurous odors".
Mad Micas: "1 tsp per pound of oils" for its red iron oxide, ultramarine blue and green chrome oxide; "Stable in high pH".
Lovin Soap, colouring soap: pigments "color lather if too much is used"; natural colourants "do tend to fade".
LANXESS Bayferrox technical data sheets (2024–2025), tamped density: red 110 M and 130 M 0.6–1.1 g/mL, yellow 920 0.2–0.6, black 318 M and 330 0.8–1.2. EFSA FEEDAP (2016): apparent density about 0.7 kg/L red, 0.4 yellow, 0.7 black.