Roman frescos became famous for their artistic style; sometimes crude, often simple, at other times fantastically complex. The Roman architect Vitruvius deplored this fashion for imaginative resetting and condemned such works as “paintings of monstrosities.”

 In Vitruvius’ opinion, the only way to appreciate artistic excellence in his day was “by the use of colours and the brave show they make.” This could explain why Vitruvius — and Pliny the Elder after him — left us with such a detailed catalogue of the pigments available to the Roman palette.

Natural or artificial, readily available or rare — the analyses of modern technology now supplement our knowledge of ancient Roman colours. These analyses now enable us to fully appreciate the full range available to Roman artists — and how they made us of them to create colour and tone in wall paintings.

Red Pigments in Ancient Roman Paint

Red was one of the most popular colours in Roman wall art, finding itself applied to street walls as well as frescos. Pliny and Vitruvius describe a variety of red pigments. Some were standard parts of the artist’s palette while others were so costly the patron had to supply them specially. 

First, there were the abundant and cheap red pigments. These were mainly naturally occurring “red earths”, “found inabundance in many places.” Such colours were generally red iron ore based and included ruddle, red ochre and hematite. Modern analysis using electronic spectroscopy has proven these to be the most prolific red pigments in use. Ruth Siddall, in her study of Pompeian frescos, also found that the Romans used madder root and crushed insects.

But the most desirable red was the artificially produced vermilion. It was also the most expensive —16 times more costly than red ochre, which cost only two denarii per Roman pound.

The Romans made vermillion from cinnabar, a naturally occurring mineral ore. To produce the pigment, which was one of the purest, brightest reds, they washed and heated the ore, most famously in factories in Rome near the temples of Flora and Quirinus.

But vermilion was unstable, turning black in sunlight, which was why Vitruvius warned against its use for “open apartments such as peristyles or exedrae.” As a solution for those determined to use the colour outdoors, he suggested treating the completed paintwork with a mixture of melted pontic wax and oil buffed with linen cloths and sealed with candle wax.

But despite the emphasis on the desirability of cinnabar-based vermillion, modern analysis has proven that the Romans rarely used it in its pure form. Instead, the Romans mixed cinnabar with other pigments — to cut the expense and possibly stabilise the colour. Vitruvius mentions lime as one such additive but Siddall and Edreira et al. have shown that the Romans cut pure cinnabar with the cheaper red oxide-based pigments, such as hematite and red ochre.

 Ochre/Yellow Pigments in Roman Wall Paintings

Yellows and browns were also staples of the Roman artist, forming backgrounds to wall paintings and also providing flesh tones to figures. Yellow ochre — made from a clay containing yellow iron oxide — was the most commonly used yellow pigment, according to both historical sources and modern studies.

But other yellow pigments were available. Vitruvius mentions orpiment, an arsenic-based ore, which gave a clear, bright yellow paint. Spectroscopy has identified others. Mazzocchin et al. have identified Limonite, a yellow iron ore as the pigment used in Italian villas. The various studies have also revealed that different shades of yellow were achieved by blending with other colour pigments.

Ancient Rome’s Greens and Blues and Purples

Once again, the choicest pigments in this range were rare and beyond the purse of most patrons. According to Pliny, “rich blue, vermilion green, indigo” were expensive and outside the artist’s usual palette, with indigo cost 20 denarii per pound.

These highly desirable pigments came from various natural sources. Besides indigo, Vitruvius and Pliny list blue paints such as Armenian Blue, made from ground azurite and Tyrian purple made from sea snails.

Modern studies have confirmed the use of some of these precious materials as pigments. Traces of lapis lazuli and malachite have been found in Pompeian paint pots, although Tyrian purple has not yet been identified. But despite their presence, they are rarely found in frescos. Instead, blues, greens and purples were commonly manufactured from other, less expensive pigments.

 The historical sources describe some of these alternatives. Vitruvius, for example, explains how to make an imitation Malachite green by mixing a blue dye with a plant called dyers weed to obtain “a most vivid green” known as dyer’s malachite green. Heating sheets of copper over sawdust after steeping them in vinegar could produce verdigris green. Pliny also mentions a pigment called green earth, found to occur naturally around Verona and Nice. Edreira and Mazzocchin et al. have proven this was the most common green pigment in use.

In the blue range, indigo could be replaced by dying Selinusian or Anularian chalk with woad. But the most common type of blue pigment confirmed by modern analysis was a manufactured substance called Egyptian Blue. Vitruvius describes how “sand and the flowers of natron are brayed together so finely that the product is like meal and copper is grated by means of coarse files over the mixture like sawdust to form a conglomerate.” This mixture was then rolled into balls and dried, put into an earthenware jar and heated.

 As for purple, if shellfish were unavailable, it could be produced from burnt ochre, heated and quenched vinegar. Vitruvius also advised “dying chalk with madder root and with hysginum” and using the strained water of dried violets mixed with chalk or bilberries mixed with milk. Modern analysis of frescos in Pompeii and Spain also shows that a wine coloured shade of violet was produced by heating hematite.

But greens and purples could also be obtained by mixing other colours. Spectroscopy from various studies has shown how green was achieved by mixing Egyptian blue and yellow ochre. According to Siddal, purple could be made by mixing hematite and Egyptian blue or madder and indigo.

Black Pigments in Roman Frescoes

 Black was “Indispensable in many works,” according to Vitruvius and indeed black probably appeared in every wall painting one way or another, whether as a mixer, a dramatic background or part of the simple décor of service areas.

The most common type of black pigment described by historical sources and backed up by studies was carbon-based, i.e. made from the soot. The Romans considered Resinous pinewood to be the best source. Pliny mentions how the Romans built special factories which prevented the discharge of “their smoke into the atmosphere.”

Understandably, factory-manufactured blacks were expensive. But there were cheaper versions. Pliny mentions how “painters have been known to dig up charred materials from graves,” to create a suitable black. Vitruvius describes a less extreme alternative, suggesting painters burn their own “shavings and splinters of pitch pine,” which could then be ground up and mixed with gum in the usual way to create black paint. But he also mentioned that roasted wine lees were used for “a colour even more delightful than ordinary black.”

White Pigments in Roman Paint

 White paint could form an economic backdrop for cash strapped homes or unimportant rooms, and also a simple canvass for intricate designs in high-status homes. Spectroscopy has confirmed that the Romans made most whites from chalky calcium carbonate, with sources from limestone, mollusc shells or even bird shells in evidence.

According to Pliny, Melian white was the most sought-after, carbonate-based pigment. But Vitruvius also describes the production of a white lead pigment, manufactured from sheets of lead laid over wood shavings and steeped in vinegar. Archaeologists have identified this type of white pigment in Pompeian frescos.

 But again, modern analysis of frescos has shown that natural whites could be improved upon, with one popular trick being to add a dash of Egyptian Blue to sharpen the brightness.

Ancient Roman Colours: “A Brave Show”

Modern technology has confirmed much of the information about the use of Roman paint pigments described in the ancient sources. But analysis has also given us a clear picture of the pigments commonly used. The Romans rarely used expensive pigments such as cinnabar, indigo and malachite — or else used them in combination with some of the more accessible, less costly pigments, undoubtedly to cut costs.

But colours were also mixed much more frequently than suggested by Pliny and Vitruvius, to imitate the more expensive pigments and vary shade and tone. These colours created effects that prove Roman artists did indeed use colour to make “a brave show” of their art.

Sources

Pliny the Elder, Natural History, Penguin Books

Vitruvius On Architecture

MC Edreira, M J Feliu, C Fernandez-Lorenzo, J Martin, (2002)“Spectroscopic analysis of Roman wall paintings from Casa del Mitreo in Emerita Augusta, Merida, Spain” Elsevier Science.  

G A Mazzocchin, F Agnoli, M Salvadori, (2004) “Analysis of Roman age wall paintings found in Pordenone, Treiste and Montegrotto.”  Elsevier ltd  

Ruth Siddall, (2006) “Not a day without a line drawn: pigments and painting techniques of roman artists.” Focus.