Technique and Conservation

Giotto's pictures are made of things that behave differently: wet plaster, dry paint, wooden boards, gold leaf and, in some works, glass. Their convincing bodies and rooms depend on the way these materials were prepared and combined. The same materials also help explain why one face remains beautifully modelled while a nearby robe looks thin, why a golden ray has disappeared, and why cleaning can change our understanding of an entire chapel.

There is no single material recipe that can be applied to everything bearing Giotto's name. The Scrovegni Chapel in Padua, the Bardi and Peruzzi chapels in Florence, and the surviving painted panels preserve different working decisions. Conservation makes those differences clearer. It brings us close to the sequence of making, from a carpenter's joint to a painter's adjustment, while also revealing how much later damage and intervention separate a medieval painting from its present appearance.

A useful starting point is to distinguish three questions. What can we see? What has examination established about the physical object? What do those findings suggest about the artist and workshop? A dark blue surface can be described by looking; naming its pigment requires other evidence. An incision can establish the position of a planned architectural line without identifying the person who cut it. A recovered face can strengthen a stylistic comparison without settling every question of attribution. The interest lies in bringing these kinds of knowledge together carefully.

Painting on wet plaster at Padua

In true fresco, or buon fresco, pigments dispersed in water are applied to a suitably fresh lime plaster. As the plaster carbonates, the colour becomes bound into its surface. The painter therefore works with a changing material. Plaster that is too wet resists the brush differently from plaster approaching the end of its useful working time; the colour of the drying wall also changes. Planning includes anticipating the finished appearance of a stroke made under quite different conditions. ^[1]

The wall is prepared in stages. A rougher underlying coat, the arriccio, provides a basis for establishing the composition. A smoother finishing plaster receives the painting. A giornata is a portion prepared for a working interval, its size adapted to what could be completed while it remained suitable. A relatively uncomplicated background might occupy a large area; a difficult face could require a much smaller one. These boundaries record practical choices, although they do not translate straightforwardly into a diary of the artist's movements. ^[1]

The distinction matters when imagining a large cycle in progress. We can follow a scene as a continuous event, moving from a face to an outstretched hand and then across an empty sky. The painters had to produce that continuity through separate operations. Plaster preparation, drawing, painting and later finishing needed to meet without making the picture look assembled. A small working area could contain something visually decisive, while a much larger area might establish the quiet space around it.

The Istituto Centrale per il Restauro's explanation of the Padua techniques warns against equating a count of giornate with a count of elapsed days. Complexity, conditions and the number of painters all affect the calculation; preparation and finishing add work that the plaster map alone cannot measure. ^[2] A boundary can help establish which portion came before another. It cannot, on its own, tell us whether Giotto stood at that point on a particular morning, or whether another painter was working elsewhere at the same time.

Drawing also has a material history. Snapped coloured cords could establish straight divisions; incisions could guide geometric forms; painted lines could set out figures. Such evidence makes the chapel's orderly spaces less mysterious without making them less impressive. The apparent ease of a building's placement comes after decisions about measurements, edges and the relation between one painted compartment and another. In a successful picture these decisions support the story so effectively that they tend to disappear from our attention.

Looking at the Padua Crucifixion, the long horizontal cross and Christ's extended arms hold the upper field together. Below, the mourners cluster to one side while the figures around the garment form a different knot of action on the other. The blue between these groups is an active interval: it separates bodies, gives the flying angels room and makes their directions legible. Technical study asks how that blue was applied and preserved. Close looking asks what the interval does within this particular scene. Both questions are necessary, and neither can answer the other entirely.

Dry finishes, blue and the richness of a wall

Fresco painting did not end when the last fresh plaster dried. Some effects required further work on the surface. Painting a secco means painting on dry, or substantially dry, plaster, with an appropriate means of adhesion. At Padua, azurite blue and metal-leaf decoration belong to the account of these supplementary operations. A painted preparation could establish the tone beneath a later blue, while gilding supplied a kind of brightness different from a light-coloured pigment. ^[2]

The official report of the ICR programme describes a particularly varied technical ensemble: fresco alongside tempera using animal glue and egg, lime painting on a dry surface, the treatment of imitation marble, and oil where lead white was used. Its recorded dates for the principal mural campaign are 3 July 2001 to 18 March 2002. ^[3] These are findings about the Scrovegni decoration and its treatment, rather than a universal list to be attached to every work associated with Giotto.

They also change the way the chapel can be imagined. A wall that now reads principally as broad fields of colour could originally combine different surface effects. Light could be absorbed by one passage and caught by another. The definition of a halo might depend on the meeting of paint and metal rather than colour alone. A fictive marble panel invites comparison with stone, yet it remains part of a painted architectural setting. The materials take part in the chapel's movement between ordinary substances and represented splendour.

Blue is particularly vulnerable to loose description. The word names an appearance, not one mineral or one method. It is possible to see blue in the sky of a reproduction without knowing whether that photograph accurately records its present hue, how much finishing survives, or what preparation lies beneath it. Where a technical account identifies azurite or a dry application, the identification belongs to the examined passage. It should not spread automatically to every blue mantle, sky or cross in the painter's surviving work.

The same care is needed with exposed preparations. When an upper layer disappears, the remaining surface may display an earlier stage rather than a deliberately finished colour. Such a passage can be exceptionally informative about the order of work. It can also be misleading if treated as a complete statement of Giotto's intended palette. A preparatory tone had a job within a layered construction; its present prominence may be an accident of survival.

These distinctions give loss a visual consequence beyond the small area where paint is missing. If a richly finished robe becomes pale or patchy, its relation to the neighbouring face changes. If a luminous ornament disappears, the surrounding architecture may look quieter. Damage can alter the rhythm of attention across a scene even when the principal figures remain identifiable. Conservation history is therefore part of understanding composition, as well as part of caring for the wall.

The Peruzzi Chapel: different techniques within one room

The Peruzzi Chapel is an especially useful warning against describing an entire interior with one technical label. Cecilia Frosinini's conservation report explains that its narrative scenes were painted a secco, while the vault appears to have begun in buon fresco. The ribs and decorative bands, grey preparations for azurite, and imitation-marble dados provide further evidence of fresco work. Even within a single commission, method changed according to the area and task. ^[4]

Its plaster was applied in broad horizontal portions called pontate. These span the walls and divide individual scenes horizontally. Patches associated with the holes for scaffolding beams survive as another kind of evidence. Frosinini discusses the possibility of platforms allowing simultaneous work on opposing walls, but also acknowledges that the holes may have been inherited from the masonry campaign. Their alignment supports an investigation; it does not compel only one reconstruction of the scaffold. ^[4]

For a visitor, these distinctions help explain an uneven experience. Some architectural divisions are strongly legible while bodies and draperies can seem depleted. In the Ascension of Saint John the Evangelist, the saint rises diagonally through a carefully articulated enclosure. The stepped walls, upright columns and contrasting groups of witnesses still organise the scene, but much of the upper receiving company is difficult to follow in ordinary light. We can recognise the upward movement without possessing the full original richness of its destination.

The appearance of the worn surface does not prove that the picture was conceived as an austere arrangement of outlines. Frosinini's ultraviolet fluorescence investigation made modelling, folds, expressions and parts of the receiving group much clearer in photographs. The complete photographic campaign took place in November 2012. These images recover information about surviving material whose response differs under ultraviolet illumination. They do not physically return missing paint to the wall. ^[4]

That difference is easy to lose in the language of discovery. A figure can reappear in a scientific image while remaining faint to the visitor. Its improved visibility can transform interpretation: a gesture, a fold or a spatial relationship becomes available for study again. Yet the image remains a record made under particular conditions. Its colours should not be mistaken for the colours that a medieval spectator saw, and its clarity should not be read as the result of repainting the chapel.

Frosinini is equally explicit about limits. Later treatments and contamination complicated the analysis of original binding media. A proteinaceous binder was detected more generally, probably egg, while lipids appeared in some areas; explanations involving whitewash and chemical alteration remained hypotheses. The unusually strong ultraviolet response also had several possible causes, including interactions between original and later materials. ^[4] The report's qualifications are part of its value. They prevent a striking image from becoming an overconfident claim that every dry passage contains one securely identified binder.

The Peruzzi evidence encourages a particularly attentive kind of looking. Follow a figure's surviving silhouette, then notice how little modelling remains inside it. Compare that with a neighbouring area where a face or garment still carries more information. The difference may affect how forcefully a character occupies the room. Scientific images can help us understand that disparity, while the visible wall preserves the encounter with what has survived in place.

The Bardi Chapel after the restoration completed in 2026

Next door, the Bardi Chapel presents a different conservation history and a newly clarified appearance. The Opera di Santa Croce announced completion of its four-year restoration on 11 September 2026. Conservation addressed unstable plaster and paint, cracks, salts, deposits and altered materials, as well as the visual interruption caused by many small losses. The completed intervention also clarified the contribution of several painters working under Giotto's direction. ^[5]

The earlier Opificio examination had already established an important distinction: the giornate show a fresco basis adapted to backgrounds and figures, but ultraviolet examination revealed extensive dry work, including portions of buildings and whole garments. That record also states that accumulated restoration materials prevented a precise identification of the binder. ^[6] Its account belongs to an earlier investigative phase. Its references to a future restoration should not be read as the chapel's present status.

The most recent account of the working process adds a telling observation. Small tests of colour survive in areas that were destined to receive dry finishing; the loss of the covering paint has exposed marks that were not meant to remain visible. The same account describes work proceeding from upper levels downward, with finishing and metal leaf completed before the scaffold moved below. ^[7] These details make the workshop tangible: decisions about colour and access were embedded in the making of a coherent narrative environment.

They also explain why the surviving surface can be deceptive. An exposed test stroke might look abrupt beside a smoothly painted head because the two occupied different stages in the process. The rawness of the first is evidence of interruption by loss. It cannot be used as a fair measure of the finish the workshop intended. Equally, the fact that one passage is beautifully preserved does not allow the missing finish of another to be reconstructed with certainty.

The Bardi walls have passed through several kinds of alteration. Limewash concealed them before 1730. Nineteenth-century funerary monuments damaged the lower scenes; rediscovery in 1851 was followed by Gaetano Bianchi's extensive completion and unifying treatment. Procacci and Tintori removed nineteenth-century repainting in the campaign identified in the current history as 1957–59, preserving some additions separately as documents. The latest treatment keeps the large losses associated with the monuments recognisable while restoring essential architectural continuity through distinguishable integration. ^[8]

This history helps distinguish cleaning from reconstruction. Removing an altered coating can reveal surviving paint. Removing a nineteenth-century completion can reveal a loss. Filling a gap can support the surrounding material. Colouring that fill can reduce its visual dominance. These actions may all occur within a restoration, yet they have different effects on what the spectator sees. A newly continuous cornice may include an intelligible modern completion; a newly legible face may consist of paint that was already there beneath obscuring material.

The aim of legibility is especially consequential at Bardi because the scenes belong to an architectural ensemble. Painted framing connects one event with another and relates the walls to the vault. A scattered field of small bright losses can repeatedly interrupt that connection. Reducing their interference may let the eye follow a room or a group again, even while the losses themselves remain identifiable. The spectator gains a better sense of the whole without being offered an imaginary undamaged chapel.

What diagnostic images reveal—and what they do not

The Bardi investigations show why conservation uses several forms of examination. Diffuse light records the general surface; raking light brings out relief, incisions and irregularities. Ultraviolet examination helps distinguish materials and interventions. A three-dimensional model brings observations into a common spatial record, while investigations of the wall and plaster address hidden discontinuities. These are different questions asked of the same building. ^[9]

An especially vivid result concerns the Apparition at the Chapter of Arles. Mapping the distribution of lead with X-ray fluorescence made it possible to recognise the image of a crucifix on the chapter room's rear wall, no longer visible to the naked eye. ^[9] A scene whose setting had become visually impoverished consequently yields information about a lost element of its represented interior. The evidence is a distribution of material read in relation to the picture, rather than a new cross painted onto the wall.

This is distinct from an X-radiograph, which is also useful for understanding wooden structures, and from infrared reflectography, which can disclose certain kinds of drawing beneath paint. The name of a method matters because its image has a particular physical basis. A black-and-white technical image is not simply an exceptionally clear ordinary photograph. Different materials respond differently, and information absent from one type of examination may emerge through another.

The London Pentecost offers a useful caution. Its underdrawing is clearer under a microscope than in infrared reflectography, which Dillian Gordon relates to the possibility of a non-carbon drawing material such as iron-gall ink. ^[10] A weak infrared response therefore need not mean that the painter worked without a drawing. The question is what that particular examination can register in that particular object.

Scientific results are also used to revisit interpretation. On the Bardi vault, an object that Bianchi had made legible as a red-covered book in the allegory of Obedience has been identified after cleaning as a second yoke, corresponding to the one on the figure's shoulders. ^[7] The change affects the allegory's action: the figure offers something to the viewer. Conservation here alters an art-historical reading by clarifying the evidence on which the reading depended.

A changed interpretation is not a failure of looking. It is a reason to look again. Earlier spectators encountered a different surface, and earlier scholars worked with different photographs and technical information. The most responsible account makes those conditions visible. It distinguishes a documented finding from an explanation still under investigation, and a recovered detail from a complete reconstruction of the original scene.

Wooden paintings: construction before colour

A panel painting begins with a different set of physical decisions. Its support must carry a prepared painting surface while accommodating joints, attachments and the form of the object. A large cross is both an image and a substantial structure intended to be seen in an architectural setting. A small narrative panel may preserve clues to a much longer ensemble that has been divided among collections. The back and edges can be as informative as the picture's centre.

The white preparation is itself an important material. Gesso is gypsum combined with an animal-glue adhesive, worked to provide a smooth ground for painting and gilding on wood. It can be incised and can also carry relief decoration. ^[11] A panel painter therefore meets a prepared surface with its own qualities, rather than painting directly into the grain of the board. A sharp line in a halo or border may be cut into that preparation, beneath or through the metallic finish. Understanding which layer carries a mark helps distinguish the construction of the support from the construction of the image.

The Ognissanti Crucifix supplies a particularly clear example. The Opificio records seven-centimetre poplar boards, a carved limewood frame, fir and chestnut bracing and a total weight exceeding 400 kilograms. Linen and parchment strips intervene at vulnerable points beneath the gesso preparation. X-radiography established that Christ's halo was reduced and lowered after the fabric had been applied but before the gesso layers. ^[12]

That sequence places a change within the making of the object. It is more informative than simply observing that the halo looks carefully related to the head. The change preceded the visible painted finish, so it belongs to the workshop's construction and adjustment of the cross. It also reminds us that proportion could be reconsidered through the manipulation of real pieces of wood, as well as through a line drawn on a surface.

The finished cross makes its material complexity visually coherent. Christ's pale torso extends across a saturated blue field; around it, the gilded outline swells into the lobed terminals containing Mary, John and the blessing Christ. The decorated border does not feel like an incidental surround. Its repeated forms give the large object a rhythm, setting the long bodily curve against a more regular framework. The image has to hold together from below and at a distance, while offering smaller details to closer attention.

Here the relationship between naturalism and splendour is particularly direct. The chest, abdomen and bent knees suggest a body's weight, while the halo and framing establish another kind of presence around it. One surface can ask us to notice suffering flesh and precious ornament at once. Describing the object only as a realistic representation leaves out much of what it does as a suspended, shaped and decorated cross.

The Ognissanti account also identifies carbon drawing, incised and gilded decoration, layered blue and green flesh preparations, together with coloured glass and mirror material in the halo. ^[12] These findings explain the resources available to this particular workshop operation. They cannot be carried across without evidence to the Santa Maria Novella, Rimini or Padua crosses. Similar subjects and formats do not guarantee identical supports, paint layers or histories of treatment.

Gold, flesh and an adjustment in the Washington Madonna

The Washington Madonna and Child gives a smaller, more intimate example of the relation between material construction and visible form. Mary holds a white rose while the child reaches towards it and touches her hand. His body turns across the dark mantle; her long fingers connect the flower with the support of his weight. Gold frames the encounter, but the touches between hands direct attention into the figures.

The National Gallery of Art's technical summary records a single vertical-grained poplar board, fabric beneath the white gesso, and a green-earth layer followed by red bole under gilding. Figure outlines and decoration were incised. Green preparation and verdaccio helped develop the flesh, which was built in thin layers. Infrared examination disclosed an adjustment to the child's face, tilting it upward through shifts in the eyes and ear. ^[13]

The Washington Madonna’s hands and rose in a normal photograph of the surviving painted surface. National Gallery of Art, Washington, Samuel H. Kress Collection,1939.1.256. Image source. Public domain. Proportionally reduced reproduction; no colour or content enhancement.

The visible result encourages us to see that adjustment in relation to the exchange. A slight change in the angle of a child's face can affect how firmly he addresses the space beside him, how his head sits on the torso, and how the two figures relate. Technical examination identifies the alteration; interpretation explores its consequence. We cannot recover every reason for the decision, but we can recognise that the image emerged through choices rather than arriving fully fixed at the first drawn stage.

Bole, the term used in the catalogue, names a clay layer beneath gold leaf. Red bole is common, and its warmth affects the appearance of the thin metal above it. ^[14] It is one more reason why a golden surface cannot be understood from the gold alone. In Washington the recorded sequence includes green earth below red bole; the order matters as much as the names.

Gold and flesh also involve different kinds of work. The patterned halos organise circular zones behind the heads, while fine tonal transitions give the cheeks their turning form. Their meeting is sharply visible, but the layers responsible are largely concealed. A description based only on the final colour would miss the distinction between an incised boundary, a prepared gilded surface and paint built through successive applications.

This example makes comparison especially useful. The green flesh preparation documented in Washington should be held beside the London Pentecost, where Gordon records thin flesh painting without green underpaint. ^[10] The variation matters more than a neat universal formula. To identify a work with Giotto or his workshop is not to claim that every face beneath that name was constructed with the same materials in the same order.

The London Pentecost: lost rays and a divided board

The Pentecost in London is a small egg-tempera painting on poplar, catalogued by the National Gallery as Giotto and Workshop. It is a separate physical work from the Pentecost at Padua, despite their shared subject. In London, the gathered heads rise above an ornamental barrier and a closed gate. The upper architecture offers a sequence of three gables and a patterned ceiling, turning a compact square into an unusually elaborate interior. ^[10]

The London Pentecost panel, NG5360, in its visible present surface.

The medium label is equally specific. In egg tempera, egg yolk binds the pigment. The broader historical word tempera can refer to more than this one binding medium, so a catalogue that identifies egg tempera supplies information beyond a general label of tempera painting. ^[15] The London panel belongs to a different physical category from a fresco wall, even where the painter faces a related problem of arranging heads, architecture and heavenly light.

Gordon's examination distinguishes the present rays from traces of an earlier system. Original rays of gilded tin have largely disappeared; their incised guides and scattered material traces survive. The more conspicuous later rays were applied over cracks. The distinction changes the imagined surface: the original metal strips would have stood above the painting and gold halos, giving the descent of the Spirit a physical prominence. ^[10]

The damage is therefore bound up with the subject. An almost vanished material once helped articulate the connection between the dove and the apostles. The narrative remains readable, but part of its original visual emphasis has been diminished. A modern diagram can indicate that lost arrangement, provided it is understood as explanatory documentation. It does not make the ordinary surface an untouched record of the first painted scheme.

The panel's reverse opens a further history. Marks of a former batten, traces of preparation and the remnants of fictive porphyry suggest an object with a considered back as well as a front. More decisively, comparison of wood grain in X-radiographs connects it with six other narrative panels, originally painted on a continuous board approximately 308 centimetres long. London and the New York Nativity and Epiphany occupied opposite ends. ^[10]

That is stronger evidence for physical association than a resemblance between faces or buildings alone. It gives the separated pictures a common material history. Their exact original function remains a further question: Gordon favours an autonomous dossal, whereas a predella has also been proposed. A reconstructed long arrangement can be persuasive without supplying the missing medieval location or resolving the division of labour among painters.

Cleaning, integration and the next generation of care

Cleaning brings unusually immediate changes, but it is an exercise in discrimination. At Ognissanti, the dark non-original coating contained plant gum and calcium oxalates. Removing it was difficult because the underlying preparation was highly water-sensitive. Controlled emulsions and microscopic observation permitted selective treatment while retaining a thin varnish considered probably original. Differentiated reintegration and a new supporting structure addressed appearance and display as well as preservation. ^[12]

The distinction between an unwanted dark coating and a potentially original varnish is crucial. Age alone does not tell the conservator what a layer is or what to do with it. The surface has to be understood as a sequence. Nor can a darker historical photograph be treated as proof that Giotto intended a subdued palette. It records an appearance at a particular stage in that sequence, under particular conditions of photography.

The Santa Maria Novella Crucifix has its own treatment history. The church archive records its return in March 2001 after prolonged conservation at the Opificio. A subsequent custodial account describes maintenance in December 2017: the cross was lowered for examination, lifting colour around board joints was secured, dust was removed, and small losses were toned with watercolour. ^[16] These are separate events from the Ognissanti treatment, with their own object and purpose.

Giotto's Crucifix in Santa Maria Novella

The modest scale of that maintenance is instructive. A restored work continues to inhabit a building, collect deposits and respond to its environment. Accessible examination and secure suspension make future care possible. At Padua, the official chapel account describes annual checks and programmed maintenance following the 2001–02 campaign. ^[17] The dramatic public moment of a restoration's completion belongs within a much longer responsibility to observe, compare and intervene when needed.

Conservation changes the questions we can ask of Giotto. We can follow an adjustment made before gesso covered a cross, recognise dry finishing where a wall has lost its richness, or reconnect panels through the grain of a sawn board. We can also understand why an apparently clear detail once led viewers astray. Returning to the painting with that knowledge makes the encounter more specific: this body, this halo, this room, made through particular decisions and surviving through a particular history.