Painted walls in Pompeian houses could suggest gardens beyond the room or columns supporting an imaginary structure. Roman decorators achieved these effects through prepared plaster, mineral pigments, drawing and carefully judged light and shadow. Painted interiors framed meals, visitors, domestic worship and ordinary household activity. Much of what we know about them survives because the eruption of Vesuvius covered Pompeii and other communities around the Bay of Naples in AD 79.
fresco refers to painting with colour applied while lime plaster is still damp. Roman decorators used this method extensively, although many finished walls also incorporated details painted after drying, moulded stucco, polishing and protective treatments. Work began before any pigment was applied: workers prepared the masonry, mixed plaster, established the design and planned the order of decoration. A decorated room was the result of several connected crafts.
Ancient instructions and excavated materials document those crafts. The Roman architect Vitruvius described preparing plaster and applying colour; excavated pigment pots and walls left unfinished show the work at different stages. Modern scientific tests can identify particles of pigment, successive painted layers and, in some cases, their binding media. The combined evidence explains Pompeian fresco techniques while showing why individual workshops need not have followed precisely the same recipe.
Preparing the Wall: Lime, Sand and Several Layers of Plaster
Painters needed a smooth, stable base for the decoration. Bare brick and stone were uneven and absorbed moisture unpredictably, so workers first built up a base of lime mortar. Limestone was heated to produce quicklime, which was carefully combined with water to make slaked lime. Sand, fragments of crushed pottery or other aggregates could then be mixed in to produce plaster. Coarser early coats levelled the wall and gave later, finer coats a surface to grip; the quality of this foundation affected the decoration above it.
Vitruvius discusses the process in Book 7 of On Architecture, written in the late first century BC. He called for well-slaked lime, successive applications of sand mortar and fine outer coats containing powdered marble. Improperly prepared lime, he warned, could cause blistering, while badly executed thin layers were vulnerable to cracks. The passage tells us what a Roman technical writer regarded as good craftsmanship. It cannot establish that every wall excavated at Pompeii was built to Vitruvius’s specification.
Excavated plaster often has fewer layers than Vitruvius recommended. In their 2021 study of Roman wall painting, Monica Salvadori and Clelia Sbrolli found that excavated examples more commonly have three or four preparatory layers, although especially elaborate houses can show additional ones. Conservators use the Italian term arriccio for rough plaster and intonaco for the finer finishing coat. These labels help to describe the surviving sequence without implying that all Roman teams used a single prescribed number of coats.
The final plaster could contain powdered marble or calcite to make a pale, smooth surface. Workers compressed and polished it with floats and related tools. A level finish made fine lines easier to draw, affected the spread and attachment of pigment, and determined how light reflected from the wall. The result could shine without any wax. Vitruvius also recognised the danger of damp penetrating plaster. He recommended measures including air gaps, drainage and mortar containing crushed pottery to protect decoration from moisture rising through the masonry.
Why Painting on Wet Plaster Lasted
The carbonation of the plaster helped pigments remain embedded after drying. Fresh lime plaster contains calcium hydroxide, which reacts with carbon dioxide as the surface dries and forms calcium carbonate. Mineral pigment mixed with water and brushed onto a suitably damp wall can become trapped in this hardening carbonate layer. The pigment particles themselves do not turn into another coloured compound. They are held by the developing structure of the plaster. This technique is known as buon fresco, or true fresco.
Painters worked within the time that lime plaster remained damp enough to accept colour. They could not simply paint a large wall over an unlimited number of days without preparing new areas. Conservators use giornate for the boundaries of daily patches and pontate for horizontal areas associated with scaffolding levels. The words are modern Italian analytical labels, with no implication that Roman craftsmen called them that. The Royal Society of Chemistry’s teaching resource explains the relevant carbonation reaction.
The working time of freshly laid plaster varied from one room and day to another. Temperature and humidity mattered, as did the plaster’s thickness, lime composition, degree of polishing and the difficulty of the intended picture. A broad area of colour might be completed quickly, whereas a face or architectural ornament demanded finer control. Mistakes could sometimes be addressed by preparing a replacement patch, adding another layer or applying paint differently after drying. The process imposed limits without making every error permanently uncorrectable.
Lawrence Alma-Tadema, a nineteenth-century painter, painted idealised views of Greek and Roman interiors, including The Siesta. These Victorian reconstructions can suggest the appearance of a finished classical setting, but they reveal little about the actual order of work in an ancient workshop. Excavated plaster left unfinished is more useful for understanding that process.
Drawing the Design Before Adding Colour
The team mapped the scheme before painting. A wall might have a dado or lower band, a central field divided into panels and an upper area carrying ornament, figures or imagined architecture. Rulers, cords and plumb lines provided straight guides. Snapping a pigment-covered string against the plaster could leave a line across its surface, a method supported by marks identified at Pompeii’s Sarno Baths and elsewhere. A compass supplied circles, and sharp tools could incise the outlines of figures, borders or columns.
Painters often outlined complex scenes before adding colour. An artist could brush red or yellow ochre onto the pale outer coat, producing a preparatory drawing that scholars call a sinopia. Unfinished sections sometimes preserve these lines, as do places where overlying colour has disappeared. They were not necessarily drawn on an earlier rough coat and subsequently concealed beneath fresh plaster. Some examples were placed directly on the fine finishing surface awaiting paint.
The published photographs and analysis of preparatory marks preserve evidence of outlines in Pompeii’s House of the Painters at Work. Vesuvius interrupted the decoration of a room after some forms had been sketched in ochre but before all its areas received their finished colour. These marks expose stages of work hidden beneath finished decoration and provide direct evidence alongside Vitruvius’s written prescriptions.
The Roman Palette: Earth Colours, Egyptian Blue and Expensive Red
Common pigments came from readily available minerals. Yellow ochre commonly contains goethite and related iron compounds, while hematite gives red ochre much of its colour. Soot and charcoal supplied black, and lime or other calcium-rich substances produced white grounds. Celadonite and glauconite provided green earth pigments. Their properties differed, including their behaviour on plaster, but many such materials were comparatively stable and less expensive to obtain than unusual imported colours.
Egyptian blue was a manufactured alternative to natural blue minerals. Its main coloured crystalline phase is cuprorivaite, a copper-calcium silicate made by firing copper-bearing ingredients with silica, lime and a flux. The technology existed long before Rome controlled Egypt. Vitruvius gives a recipe with sand, natron and copper in Book 7, chapter 11. Analyses of surviving pigment containers and painted fragments from the Vesuvian region confirm Egyptian blue alongside ochres, greens, blacks and mixtures. Manufacturing conditions varied by ingredients and furnace, making a single figure such as 900°C inappropriate as a universal firing temperature.
Roman decorators used several pigments for red walls. Iron-oxide pigment was suitable for broad fields of colour at relatively low cost, while cinnabar, a mercury sulphide, supplied brilliant vermilion and might be expensive. Vitruvius explains its preparation and warns about darkening in exposed places. Pliny the Elder distinguishes costly pigments supplied by patrons from cheaper materials covered by the painter’s contract. Price and availability therefore affected the result: a bright red surface cannot automatically be identified as cinnabar without examining the pigment.
A 2010 Raman-spectroscopy investigation by Aliatis and colleagues identified red and yellow iron compounds, Egyptian blue, green celadonite and mixtures capable of producing pink and purple shades from surviving pots and plaster fragments. Their results identified the pigments from surviving material, rather than relying on ancient colour names. A later 2025 study led by Celestino Grifa examined 26 samples, many still held in ancient containers, mainly through non-invasive methods. That research showed that painters blended materials for different colours, with Egyptian blue and red lead among the important components. One sample included baryte and alunite, a reminder that actual workshop palettes were more varied than the familiar short lists of pigments.
Pigment containers and painted plaster reveal colours mixed for particular shades and surfaces. Workers ground and weighed materials and combined them for the shade or surface they wanted. Blue might be mixed into green or purple; white could affect brightness and opacity. Different particle sizes could also change the appearance of a polished or coloured plaster ground. Some materials contained poisonous mercury or lead. Their identification tells us about workshop chemistry without making the risks of handling them disappear.
What Painters Added After the Plaster Dried
Painters also completed sections after the plaster had dried. Fine lines, highlights, figures or pigments that worked poorly on a damp surface could be added after it dried. This is a secco, meaning painting ‘on dry’ plaster. These layers generally needed a binding substance, either organic or lime-based, to hold their colour in place. Since they were attached differently from pigments incorporated into fresh plaster, the additions could deteriorate or flake away in different ways.
Chemical analyses have recovered some of those binders. A 2010 study by Durán and colleagues detected organic substances in wall decoration from Pompeii and Herculaneum, providing evidence consistent with painting on dry plaster. A 2024 investigation of paintings from a Roman house at Santa Maria Capua Vetere found materials including animal glue and resins and interpreted the analysed paintings as a secco. These are findings about the walls examined, not a demonstration that every Roman painter relied on the same binder or mixture.
Scholars also use mezzo-fresco for techniques involving nearly dry plaster, sometimes with limewater added to support further carbonation. Salvadori and Sbrolli’s review explains how such methods relate to true fresco. Fragments studied at Pompeii’s Temple of Venus show evidence of fresco and lime-painting procedures together. The categories describe methods that could occur together on a single wall.
Some pigments posed particular problems on wet plaster. Pliny mentioned colours that could not readily be used in this way, although the restriction was specific to individual materials. Egyptian blue could appear in lime-based work, whereas indigo, some purple colourants and other substances behaved differently. The colour that survives is therefore insufficient to establish the technique. A particular wall must be studied through its physical layers and the materials they contain.
Wax, Polishing and the Limits of Encaustic
Vitruvius described using wax to finish painted walls. In Book 7, chapter 9, he recommends melting Punic wax with oil, spreading it over dried walls painted in cinnabar, warming the coating and polishing it with cloth. He intended to protect an expensive vermilion pigment from the fading he associated with light exposure. His instructions concern that particular treatment, so they do not establish that every Roman wall painting was sealed in wax.
Painters could also suspend colour in wax itself. That is encaustic painting, practised elsewhere around the ancient Mediterranean. Some Roman-period mummy portraits from Egypt used wax colours on wooden panels, objects that differ materially from Pompeian plaster walls. Their survival does not prove that Roman mural workshops routinely painted rooms with molten coloured beeswax and hot spatulas. Older interpretations sometimes blurred the difference between paintings made with wax and paintings protected by a wax coating; recent research treats them as separate possibilities.
Analyses have found wax on some Roman plaster paintings. A 2018 investigation of the House of Octavius Quartio reported material consistent with a protective coating or consolidant on painted plaster there. Establishing when it was applied is a separate question. The substance might come from ancient decoration, a later conservation effort or more than one treatment, so each sample requires an assessment of its context.
Spring, painted by Alma-Tadema in 1894, shows the nineteenth-century fascination with the colour and pageantry of classical life. It is an oil painting on canvas, however, and should be understood as a later artistic vision rather than an example of Roman wall-painting technology.
A Painter’s Workshop Caught by the Eruption
Pompeii’s workplaces and interrupted decorations reveal much about the organisation of painters. At the House with Workshop, I.9.9, excavators found about 150 pigment containers together with pestles, spatulas, scales, a compass and a plumb bob. Marks on the walls may have recorded materials or the progress of work. The discoveries are discussed in the 2025 pigment study. The equipment shows how a workshop stored, prepared and supplied pigments for decoration.
The House of the Painters at Work, IX.12.9, preserves a room partway through decoration, with about fifty small pots of pigment nearby. Some lower sections were still bare, while other areas carried outlines or partly completed figures. The archaeological reconstruction describes work beginning in upper areas and proceeding downwards, with portions of the room at different stages when the eruption occurred. The uneven progress on the walls provides unusually direct evidence for the decorators’ order of work.
Preparing a decorated room involved several jobs: slaking lime, mixing colours, shifting scaffolding, spreading plaster, marking out the design, covering large background fields and painting more difficult figures. Scholars use tector for a plasterer, pictor parietarius for a wall painter and pictor imaginarius for a figure painter. Diocletian’s price edict of AD 301, written much later than Pompeii’s destruction, gave different maximum daily rates for wall and figure painters. The edict distinguishes these occupations, but cannot tell us precisely how a Pompeian team two centuries earlier was staffed or paid.
The work was probably shared among specialists, though scholars disagree about the organisation of individual crews and how permanent they were. Painters could be enslaved, formerly enslaved or freeborn. Repeating figures and familiar ornamental patterns suggest the possible use of sketches, models or pattern books. Yet no surviving complete Pompeian workshop archive demonstrates one catalogue adopted by all painters. The proposed use of such books remains a plausible reconstruction, rather than directly documented standard practice.
The Four Pompeian Styles Describe Decoration, Not Four Painting Methods
The First through Fourth Pompeian Styles classify decoration rather than plaster recipes or pigment binders. August Mau developed the system in the nineteenth century from excavated decoration at Pompeii and Herculaneum. Historians still use it as a guide to changing taste, although styles sometimes overlapped and older designs could return. Smarthistory’s illustrated discussion and the Metropolitan Museum’s survey illustrate the four categories and their typical features.
First Style walls imitate masonry built from expensive coloured stones. Popular in parts of the second and early first centuries BC, the decoration divides surfaces into panels resembling marble blocks, sometimes raised with stucco mouldings to strengthen the illusion. The fashion drew on Greek and Hellenistic precedents. Surviving rooms in the House of the Faun show how it gave ordinary plaster the appearance of prestige materials and carefully ordered stonework.
Second Style painting developed increasingly elaborate architectural illusions during the first century BC. Columns, balustrades, doorways and distant landscapes could make an enclosed wall appear to extend into another space, although painters did not employ modern single-point perspective in a uniform fashion. At the Villa of P. Fannius Synistor at Boscoreale, dated around 50 to 40 BC, a bedroom presents painted courtyards, columns, objects and views beyond the apparent walls. Painted architecture gave this small room the appearance of a much larger setting.
In the Augustan period, Third Style decoration often placed less emphasis on opening up the wall. Large fields of black, white, red or other colours became backgrounds for slender supports, candelabra, framed myths and miniature landscapes. The black-ground paintings from Boscotrecase from the last decade of the first century BC show how carefully these details could be arranged. Their fine architectural elements were decorative inventions, too delicate to be mistaken for structures that might actually bear a building’s weight.
Fourth Style painting, popular in the decades leading to AD 79, mixed features from several earlier fashions. Painters combined broad panels, imagined architecture, unusual constructions and large narrative pictures. The House of the Vettii preserves well-known examples. Owners commissioned different schemes, and the Fourth Style represented a change in fashion rather than a stage of technical perfection. Dates assigned to the four styles are approximate, and no decorative language disappeared everywhere at a single moment.
Later painters also imagined the event that preserved these Roman interiors. Edward Poynter’s Faithful Unto Death depicts a Roman sentry remaining at his station while Vesuvius erupts. Painted in the nineteenth century, it belongs to the modern reception of Pompeii, rather than to any ancient Pompeian style. Its subject and date need to remain distinct from the excavated wall decorations reproduced alongside it.
Myths, Gardens and the Rooms Where People Saw Them
A fresco’s effect depended partly on the room in which it appeared. Dining rooms, bedrooms and corridors had different light and viewing distances, and people encountered them in different social situations. Owners might pay for mythological pictures in spaces where guests gathered and use repeated bands or simpler designs in quieter areas. Budget, fashion, repairs and personal taste could all modify those choices. Even when two houses showed the same myth, their images need not have been composed or understood in identical ways.
In Book 7, chapter 5, Vitruvius lists popular painted subjects including harbours, landscapes, temples, human figures and stories from Greek epic. He also objects to invented architectural forms, such as fragile columns and buildings supported by plants. His criticism tells us something about the taste of his own day: decorators and patrons liked fantastic designs that this architect regarded as unreasonable. It is a personal judgement about proper representation, not evidence of a rule that prohibited imaginative painting.
Roman walls display episodes from the Trojan War and images of Dionysus, Apollo and other mythological figures alongside still lifes, gardens and invented buildings. An Apollo with a lyre could be recognised through his attributes, but the subject was also shaped by the colours, borders and position selected for that room. A surviving fragment may identify the god while leaving the full composition and the intentions of its patron beyond recovery.
Where a caption identifies a figure in a damaged painting, that identification remains dependent on the surviving image and its archaeological context. The lost sections cannot be reconstructed from the name alone.
Brushes, Tools and the Difference Between Walls and Pottery
Decorators employed implements for several stages of work. Floats and trowels prepared plaster; cords, straightedges, a plumb bob and compasses helped map the design; brushes, grinding equipment and pigment vessels supplied the painted detail. The 2021 archaeological review reproduces finds from the Vesuvian area, including cups for colour, a set square, compasses and a plumb bob. Tools rarely reveal their owner’s entire routine, but scratches and painted guidelines can sometimes show which instrument made a particular mark.
Painting a ceramic vessel required different materials and firing methods from painting a plaster wall. Greek red-figure pottery was decorated with clay slips whose appearance changed during controlled kiln firing. The preparation, surfaces, equipment and firing conditions did not resemble the application of minerals to Roman lime plaster. Roman painters could borrow Greek images and conventions, yet that artistic inheritance does not make Greek vase painting a form of fresco.
A calyx-krater attributed to the Greek Niobid Painter, dating to about 460–450 BCE, illustrates the distinction. The British Museum catalogue records decoration that includes the creation of Pandora. Those figures were made on pottery that underwent firing, whereas Roman frescoes were built up on plastered walls. The vessels and murals also belonged to different settings of use.
Why Pompeii’s Frescoes Survived and Why They Still Deteriorate
In AD 79, Vesuvius buried interiors beneath pumice and ash, protecting many of them from later rebuilding and exposure to the weather. Their burial accounts for the unusual number of Roman wall paintings preserved around the Bay of Naples. Burial did not create a perfectly oxygen-free environment or guarantee preservation without damage. Heat, collapsing masonry, groundwater, chemical alteration and later excavations could all harm pigments and plaster. Paintings survive in other Roman territories, but often as smaller fragments or less intact rooms.
A study published in 2018 examined painted fragments reused in a Pompeian pavement, which had been mixed into mortar before the eruption. Because they were reused in building material, their history differs from paintings left exposed on room walls. Researchers found hematite, goethite, celadonite and Egyptian blue. The analysis shows how discarded decorative plaster, buried in an apparently ordinary pavement, can preserve pigments that might have deteriorated under other conditions.
The surviving reds may differ substantially from their original shades. Cinnabar can deteriorate or lose material, and its darkening has several possible explanations. A 2022 experimental and analytical study investigated the idea that eruption heat turned cinnabar into black metacinnabar. For the samples examined, the researchers found that this mechanism did not adequately account for the observed damage. They identified other alteration products and pigment loss. Their results warn against treating the present colours of all Pompeian frescoes as identical to those visible before AD 79.
Excavation exposes wall paintings to new hazards. Rain, light, humidity, salts, microorganisms and handling may damage the plaster and pigment; earlier conservation materials can also complicate an analysis. Detached panels can be kept in museums, but paintings left on site must be protected against continuing weathering. Raman spectroscopy, X-ray fluorescence, microscopy and related methods can help distinguish original colour, deterioration and later restoration. They cannot, by themselves, recover the precise visual effect of an entire Roman room.
The unfinished room in the House of the Painters at Work preserves especially clear evidence of interrupted decoration. Ochre guidelines show where figures were intended, and beside finished areas are surfaces awaiting their final colours. The eruption interrupted the work, leaving its sequence visible in the surviving plaster. Roman frescoes emerged from the joint work of plasterers, decorators and figure painters, who prepared walls, organised compositions and adjusted their materials to the task. Incomplete plaster can tell us as much about their craft as the finished images do.
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