Glauconite burnt

Glauconite burnt is heat-treated natural glauconite: green earth (terre verte, PG23) heated until it turns a light yellowish brown with a greenish tint. It is a soft, semi-transparent khaki earth for glazes, toned grounds and muted warm mixtures in egg tempera, watercolor, oil and fresco.

Key facts

• Color: light yellowish brown with a greenish tint (khaki)
• Pigment type: Natural earth pigment (heat-treated green earth)
• Colour Index: PG23 (C.I. 77009)
• Composition: glauconite, (K,Na)(Fe³⁺,Al,Mg)₂(Si,Al)₄O₁₀(OH)₂, altered by heat treatment
• Also known as: burnt green earth, burnt terre verte
• Opacity: semi-transparent (glazing)
• Lightfastness: 8 of 8 on the Blue Wool Scale (supplier data)
• Chemical resistance: lime 5/5 (supplier data, 5 = best); strong acids partly dissolve green earth
• Suitable for: oil, acrylic, egg tempera, watercolor, gouache, fresco (lime), lime and cement plaster
• Packaging: 50 g jar · 1 kg bag

How to use

Mull it with egg yolk, gum arabic, acrylic medium or linseed oil using a palette knife or muller. Applied thinly it is transparent, so it suits glazes, toned grounds and soft warm shadows; build several layers for more coverage. It is lime-proof and can be used in fresco and to tint lime or cement plaster. Mix it with unburnt glauconite for olive half-tones, or with white for warm grays.

About burnt glauconite

Green earth turns brown when heated: at around 500 °C it becomes the warm, dark brown known as burnt green earth. This grade is a lighter khaki brown that still keeps a greenish cast. Glauconite itself is an iron-potassium mica that forms in marine sediments; its name comes from the Greek glaukos, "bluish green", and green earth has been a painters' pigment since antiquity.

Safety

Green earth is considered non-toxic, but natural glauconite usually contains some quartz (crystalline silica): do not inhale the dust. 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

Why is burnt glauconite brown rather than green?

Heating turns green earth brown. This heat-treated grade is a light yellowish brown that keeps a greenish tint.

Is it lightfast and suitable for fresco?

Yes. The supplier rates it 8 of 8 for lightfastness and 5 of 5 for lime resistance, and lists it for fresco and for lime and cement plaster.