Gabbro

Gabbro is a natural gray stone pigment powder ground from gabbro, a dark, coarse-grained igneous rock made mainly of calcium-rich plagioclase feldspar and pyroxene. It gives quiet mineral grays with a slight brownish cast for oil, egg tempera, watercolor, gouache and acrylic and, being lime-fast, it also suits fresco and lime plaster.

Key facts

• Color: gray to brownish gray
• Pigment type: Natural mineral pigment (ground rock)
• Composition: gabbro, an igneous rock of calcium-rich plagioclase feldspar and pyroxene with minor hornblende and olivine
• Also known as: black granite (trade name of the building stone)
• Opacity: semi-transparent
• Lightfastness: 8 of 8 on the Blue Wool Scale (supplier data)
• Chemical resistance: alkali 5/5, lime 5/5, acid 5/5 (supplier data, 5 = best)
• Suitable for: oil, acrylic, egg tempera, watercolor, gouache, fresco (lime), lime and cement plaster, ceramics
• Packaging: 50 g jar · 1 kg bag

How to use

Mix the powder into the binder with a palette knife or muller: linseed oil, egg yolk for tempera, gum arabic for watercolor and gouache, or acrylic medium. For fresco, make a paste with water and paint onto fresh lime plaster; the powder can also tint lime and cement plaster and, according to the supplier, silicate binders. Because it is semi-transparent, gabbro works well in glazes and thin layers: use it for stone and shadow tones, to make neutral grays with white, or to soften bright colors.

About gabbro

The name comes from Gabbro, a hamlet near Rosignano Marittimo in Tuscany: in the 1760s it was used for rocks of the Apennine ophiolites, and in 1809 the German geologist Christian Leopold von Buch gave it a narrower meaning. Gabbro has the same chemical composition as basalt but cooled slowly deep underground, so its crystals are coarse. Much of the Earth's oceanic crust is made of gabbro.

Safety

Ground rock can contain crystalline silica: avoid breathing 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

Is gabbro the same as basalt?

Chemically, yes: gabbro has the composition of basalt but formed by slow cooling deep underground, so it is coarse-grained, while basalt cooled quickly at the surface.

Can gabbro be used in fresco?

Yes. The supplier rates it 5 of 5 for lime and alkali resistance and lists it for fresco, lime and cement plaster and silicate binders.

Is Gabbro a black pigment?

No. Although the stone looks dark and is sold as black granite, the ground powder gives grays with a brownish tint rather than a deep black.