Yellow iron oxide
Yellow.
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
Yellow iron oxide is a pigment powder, the lightest of the iron oxides by volume: 0.2–0.6 g per mL tamped, in LANXESS’s data.
LANXESS; EFSA primary source
How much
- 1 tsp per pound of oils filled in Mad Micas supplier or guide
The calculator fills in 1 tsp per pound of oils: 4.3 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 ≈ 1.97 g (0.99–2.96 g)
- 1 tbsp ≈ 5.91 g (2.96–8.87 g)
- 1 cup ≈ 94.6 g (47.3–142 g)
LANXESS; EFSA primary source
INCI name
CI 77492 (Colour Index number)
- CAS number
- 51274-00-1, 1345-27-3, 20344-49-4, 52357-70-7
- EC number
- 257-098-5, 215-722-3, 215-570-8
- 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.