Morellone & Caput Mortuum Pigments

Morellone, or morello, literally means “mulberry color.” In period treatises the term is used broadly to denote purple-violet colors of both organic and inorganic origin, but today the name is primarily associated with a pigment obtained by grinding pure crystalline hematite stone (Fe₂O₃), one of the oldest and most stable pigments known to painters.

Cennino Cennini describes it in Il Libro dell’Arte (Chapter XLII) under the name amatisto, o ver amatito, noting that it is a natural stone, extremely hard and dense (prieta fortissima e soda), the same stone from which burnishing tools for gold leaf were made. He specifies that the unground stone appears black and lustrous like a diamond, but when ground on a porphyry slab with clear water, it yields a color that is pagonazzo, o ver morello (purple, or mulberry), and that the finer it is ground, the better and more perfect the color becomes. He recommends it exclusively for wall painting in fresco, where it produces what he calls a color cardinalesco (cardinal’s purple) or a hue resembling lake, and warns that it is not suitable for other techniques or binders.

The use of violet hematite extends deep into antiquity. Pliny the Elder (Naturalis Historia, Book XXXV, Chapter 20) describes usta, a burnt form of red ochre that produces a violet color, noting that the best varieties were highly prized despite technical difficulties in their application. Spectroscopic analysis of Roman wall paintings from the 3rd century CE has confirmed hematite as the principal component of violet passages, sometimes mixed with calcium carbonate or kaolinite to adjust the hue (Oliveira et al. 2002).

Recent studies (Castagnotto et al. 2021) have shown that the violet color of hematite depends on particle size: only pure, concentrated iron oxide with large crystal grains produces the purple hue, while ordinary red ochre, in which hematite is dispersed in clay and silica, remains red even at high temperatures. This confirms that Cennini’s amatito was true crystalline hematite and not red jasper (diaspro rosso), as some have suggested, since the dispersed iron oxide in jasper would behave like an ochre and yield only a red color.

Caput mortuum (Latin for “dead head”) is the artificial counterpart of morellone, produced by calcining ferrous sulfate (green vitriol, also known as vitriuolo romano) at high temperature. The process drives off the sulfur as sulfuric acid, leaving behind a residue of iron(III) oxide identical in composition to natural hematite. The term originally referred in alchemical practice to any worthless residue left after distillation, but from the 16th century onward it became the standard name for this artificially produced purple-violet iron oxide pigment. The Paduan Manuscript, collected by Merrifield, records a recipe for pavonazzo (purple) made with morello di ferro (an iron ore ground or calcined to a morello color) and vitriuolo romano cotto (burnt Roman vitriol). Merrifield further notes that German sources considered the terms Morellen Salz, Eisen Oxyd, and Caput Mortuum as synonymous.

The color of both morellone and caput mortuum varies from deep brick red to dark violet-purple depending primarily on particle size: larger, well-crystallized particles produce more violet tones, while finer particles yield redder hues. Modern analytical studies using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy have confirmed that all commercial varieties of caput mortuum are composed principally of hematite (Fe₂O₃), with color differences attributable to particle size and shape rather than chemical composition.

Both morellone and caput mortuum pigments are among the most permanent and lightfast colors available to painters, stable in all binders and resistant to light, alkali, and weathering.

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