Mars yellow

Mars yellow is a synthetic yellow iron oxide pigment powder (PY42), a pure, man-made counterpart of yellow ochre. It gives an opaque, muted ochre yellow with good tinting strength, and it is lightfast and lime-proof, so it works in oil, acrylic, egg tempera, watercolor, gouache and fresco.

Key facts

• Color: muted ochre yellow
• Pigment type: Synthetic inorganic pigment (iron oxide)
• Colour Index: PY42 (C.I. 77492)
• Composition: iron(III) oxide-hydroxide, FeO(OH)
• Origin: synthetic
• Also known as: synthetic yellow ochre, yellow iron oxide, jaune de Mars
• Opacity: opaque
• Lightfastness: 8 of 8 on the Blue Wool Scale (supplier data)
• Chemical resistance: alkali 5/5, lime 5/5 (supplier data, 5 = best); stable in weak acids, dissolved by strong mineral acids
• Suitable for: oil, acrylic, egg tempera, watercolor, gouache, fresco (lime), lime and cement plaster
• Not recommended for: ceramics or heating above about 180 °C: it loses water and turns orange, then red
• Packaging: 25 g jar · 1 kg bag

How to use

Mix the powder into linseed oil, egg yolk, gum arabic or acrylic medium with a palette knife or muller; for fresco, grind it in water and paint into fresh lime plaster. Yellow iron oxides disperse easily and, like other iron oxides, dry well in oil. With white it gives clean cream tints. Keep it away from heat, which turns it orange and then red.

About Mars yellow

Mars colors began as a trade name in the late 18th century and are named after Mars, the alchemists' name for iron. Mars yellow was made by precipitating iron salts with alum and an alkali; heating it gives the other Mars colors, from orange and red to brown and violet. Its coloring compound is the same as in natural yellow ochre (goethite), but without clay, so it is purer and more uniform.

Safety

Handle dry pigment with care: avoid breathing the dust and contact with eyes. Wear a dust mask (FFP2/N95) and gloves when working with the powder, work in a well-ventilated area and wipe up spills with a damp cloth. Do not eat, drink or smoke while working; wash your hands afterwards. Keep away from children and pets. For artistic and technical use only — not for cosmetics, food or tattoos.

FAQ

Is Mars yellow the same as yellow ochre?

It has the same coloring compound, iron oxide-hydroxide, but it is synthetic: purer and more uniform than natural ochre, which also contains clay.

What is the difference between Mars yellow and Mars yellow transparent?

Both are PY42. Mars yellow has larger particles and covers; Mars yellow transparent is made of nanometer-size particles that let light through, for glazes.

Can it be used in fresco?

Yes. The supplier rates its lime and alkali resistance 5 of 5, and iron oxides are classic fresco pigments.