The study and reconstruction of the polychromies of medieval English alabaster panels: historiography and methodology 

A brief historiography

The medieval English alabasters preserved in the south-west of France have already been the subject of several research works. However, these studies are often outdated and some are unpublished.¹ As they only marginally address questions relating to polychromy, without devoting any specific development to them, it is necessary to broaden this brief historiographical review by including the main works devoted to these works which came from across the English Channel.

Although they have been mentioned in a number of earlier studies, English alabasters have only been the subject of real research since the end of the 19th century. It was only then that the English origin of these panels, previously forgotten, could be demonstrated.² As the alabasters were scattered all over Europe, the first studies were devoted in particular to their survey and inventory. This was the case with the numerous publications by Philip Nelson and Walter Leo Hildburgh, the first of which date back to the 1910s.³ At the same time, criteria for dating the alabasters were developed, based in particular on the shape of the panels’ frames, this chronological grid primarily being the work of Edward Prior.⁴ Researchers also examined the iconography of the slabs and since the 1940s studies have been published on certain categories of alabaster, in particular on statues of the Virgin and Child.⁵ At the end of the 20th century, comprehensive inventories and classifications of English works emerged,⁶ while in recent years, context has played an increasingly important role, characterised by a burgeoning of scholarly interest in alabasters.⁷ Their function as devotional⁸ or memorial⁹ objects has thus been highlighted. At the same time, a series of studies has been undertaken to track the provenance of alabaster works, in particular in order to distinguish pieces executed in England from those created in other countries, mainly France.¹⁰

It should be noted that despite its omnipresence on the panels, polychromy is not among the major research themes outlined above, and its study remains marginal. For example, the catalogue of the exhibition devoted to English alabasters in Normandy, published in 1997, does not contain a thematic article on polychromy; yet this aspect is nevertheless detailed for two of the altarpieces exhibited.¹¹ Similarly, the book written for the Object of Devotion exhibition – a presentation of panels from the Victoria & Albert Museum in London shown in various American museums – does not include a contribution on the colour of these works either.¹² Katrin Land’s recent thesis on English alabaster statues representing the Virgin and Child discusses in a few pages the issues of polychromy where there is partial covering in some cases and complete colouring in others.¹³ Lloyd de Beer’s thesis deals with the colours and gilding of some of the works he examines, but the author makes no attempt to draw up a broader synthesis beyond these individual observations.¹⁴ The two recent collections of essays published respectively in 2019 and 2020 do not contain contributions examining polychromy from an art or culture historical perspective.¹⁵ Finally, in 2020 Kim Woods provided a broad overview of polychromy in late medieval alabaster sculptures in Europe, distinguishing between ‘minimal’ and full polychromy, but English panels are just treated briefly.¹⁶

The polychromy of alabaster is somewhat better known from an archaeometric point of view. In his 1984 book, Francis Cheetham presented a number of data collected during physico-chemical analyses of panels kept in the Victoria & Albert Museum collection in London. In 1997, Pascale Klein and Sylvie Colinart published a brief report on the Rouvray altarpiece in Rouen.¹⁷ The English reliefs preserved in Bilbao were studied in two articles published in 2008 and the painting materials of the panels were identified thanks to in situ and sample analyses.¹⁸ The other English alabasters preserved in the Basque Country were examined in two studies by Xabier Martiarena Lasa and published in 2012 and 2013 respectively.¹⁹ In 2018, a team from the British Museum, operating with state-of-the-art equipment, published an in-depth study of the pigments and binders of three panels and a statue from the museum, and proposed a reconstruction of their medieval polychromy.²⁰ Finally, in 2019, three alabasters – representing the so-called ‘St John’s heads’ – from the Burrell Collection in Glasgow were analysed.²¹

Given the quantity of panels and statuettes preserved – there are more than 2,400 – of which several hundred still retain substantial remains of their polychromy, our knowledge of this aspect of the panels remains rudimentary. There are many reasons for this lack of interest, particularly on the part of art historians. One of these is the prevalence of current aesthetic codes. Since the beginnings of art history as an academic discipline, polychromy in ancient art (Antiquity, Middle Ages) has constantly been the subject of controversy; for a long time, its very existence was at best ignored, at worst denied. The evolution of taste since the Renaissance has in fact led to a separation between the art of sculpture on the one hand and the art of painting on the other.²² This division has had strong repercussions up to today and often leads to a marked lack of understanding of the ‘unnatural mixture’ that the combination of sculpture and painting seems to constitute for contemporaries.

The limited amount of research on polychromy is also explained by the difficulty of ascertaining its initial appearance. The medieval colours are very rarely preserved in a satisfactory manner. The polychromy is generally incomplete and the pigments are more or less altered, i.e. they have lost their original colour. In order to get an idea of what the medieval colours looked like, physico-chemical analyses and the observation of well-preserved pigments under a microscope or binocular loupe are necessary. However, this equipment is not always at the disposal of researchers working on English alabasters.

The study of polychromy has also long suffered from the difficulty of reproducing works of art in colour in scientific publications. This is probably one of the reasons why, throughout the 19th and 20th centuries, colour was the poor relation of art history. It is only in recent years that this obstacle has been overcome and that colour prints are becoming common practice. 

To these three points we should add a fourth, and not the least important: the lack of knowledge about the role and function of polychromies. In most of the studies that refer to the colouring of alabaster, it is termed ‘decoration’. This expression seems to us to be an obstacle to understanding the true nature of these works. Indeed, the alabaster panels are not sculptures that have been embellished with a few brushstrokes. Rather, they are works of art that form a synthesis between sculpture and painting, even if this is not specific to English alabasters. As we shall see, the term ‘three-dimensional painting’ perhaps does them more justice than ‘painted sculpture’. In a way, alabaster could be compared to the core of an artwork by a goldsmith: it allows the coloured epidermis to be given form and relief (fig. 4). In both cases, however, this core was not intended to be seen as such. This is clearly illustrated by the very special way in which the eyes of alabaster figures are shaped. The sculptors only carve globular protuberances into the eye socket. It is then up to the painter, with a few skilful brushstrokes, to transform them into eyes and thus give life to the protagonists (fig. 5).

The loss of the coloured epidermis is therefore equivalent to a partial destruction of the works of art. In order to be able to study and appreciate the alabasters more accurately, we felt it was essential to restore as much as possible of their original coloured appearance. This book describes the research work carried out to reconstruct the medieval aspect of some alabaster panels, by determining the nature of the pigments and the different visual qualities of the colours (chromatic palette, opacity, brilliance etc.). It also aims to identify the aesthetic and symbolic principles governing the use of colours. Finally, the study attempts to expose the criteria determining how the spectator in the late Middle Ages would receive and judge these polychrome works. 

On the methodology of the reconstruction of the polychromies 

In order to achieve these objectives, a corpus of more than one hundred English alabasters preserved in the Aquitaine region was examined; most of them are concentrated in the Bordeaux area. This corpus was studied at their places of conservation, namely museums and a number of churches in the region (fig. 6 and table fig. 15). Within this corpus, three panels were selected because of the good state of conservation of their polychromy, in order to benefit from as complete a restitution as possible of their initial coloured aspect.

The study was carried out as part of a Laboratoire d’excellence research programme by a multidisciplinary team comprising an archaeometer, an art historian, an archaeologist and painter specialized in the reconstruction of ancient polychromies, 3D engineers and an opto-numerical research engineer. The Aquitaine panels were first subjected to a visual examination. Any remnants of polychromy were documented by micro-photography and then mapped by pencilling on printed images in order to obtain a first overview of the distribution of colours. At the same time, non-invasive archaeometric measurements made it possible to determine the pigments and binders used, and to study the alteration phenomena undergone by the paint layers over time. Observations were first carried out using a portable optical microscope and a Wood (UV) lamp to assess the state of the surfaces, alterations, possible repaints and fluorescent binders. For the analyses of the materials, non-contact spectroscopic methods were used. Portable spectrometers²³connected to a computer, a halogen lamp and an optical fibre were used to illuminate the works over a few millimetres and to collect the signal emitted by the pigment. The reflectance spectra obtained were recorded and compared with reference spectra in a database in order to identify the pigments. Analyses were carried out in the visible and near-infrared (400-1000 nm) and infrared (1000-2500 nm) light ranges. In some cases, in particular for the altarpiece of Saint Michel in Bordeaux, additional measurements were carried out with a portable fluorometer and a hyperspectral camera to obtain spectra of the integrity of the panels.²⁴

The results of these approaches, complemented by the consultation of ancient recipes for the manufacture of paints, provided the necessary data for the recreation of hues similar to those that medieval artists may have used. Eighty samples were created reproducing the different configurations of painted layers found on the entire corpus of New Aquitaine alabasters: the different pigments were applied to alabaster using linseed oil as a binder; gilding was carried out on different mixtures and the superimposition of several layers was reproduced. These samples made it possible to recover the original appearance of the colours, before they faded over the centuries. The alabaster copy of a medieval panel was also painted and gilded according to the findings and observations made on the original. Finally, the model samples were ‘translated’ into digital colours using a spectrocolorimeter.²⁵ The digital colours thus created were used to paint three 3D models of the alabaster panels that had been produced during the research programme.²⁶

The observations and results carried out during the carving and painting of the material copy of the alabaster panel will be detailed further in the book.²⁷ As for the digital copies, they were created using a double process combining acquisition via a 3D scanner²⁸ and by dense-matching photogrammetry. The files acquired in this way were merged into a single digital model, which made it possible both to complete the areas that were difficult to access using either of the techniques and to obtain the best possible compromise between maximum fidelity of reproduction on the one hand and, on the other, the smooth, polished appearance that the surfaces of the medieval alabaster initially had (fig. 6). These models were computer processed for digital painting²⁹ and then painted employing Autodesk’s Mudbox software, which uses a tier system to imitate the layering of the various coats of paint. Once the work on the copies is completed – this work is still in progress – comparisons between the physical and digital copies will be possible. The convergence between the visual aspect of the two types of copies, one real, the other virtual, is being improved thanks to measurements of the optical properties of the panels, carried out with a specific device.³⁰ Next, these measurements are employed to obtain a reflection model which can then be used in turn in a rendering engine, serving as a specific ‘shader’, in order to reproduce as faithfully as possible the translucency of alabaster or the reflections of gold, which change considerably according to the lighting conditions. Yet, it is the optical qualities of both alabaster and gold that are essential for the accurate appreciation of these late medieval works of art.

An archaeological chimera or the limits of the method

To what extent is it possible to restore the medieval appearance of an alabaster panel? The results that are presented here lead to a visual outcome that necessarily bears the marks of the 21st century, and not to a ‘photograph’ of the works of art as the medieval viewer saw them. We do not insist on the biases of the study induced by our own representations and mental images of the Middle Ages, which have already been highlighted by numerous studies. Let us nevertheless mention the fact that the simulation of new colours, applied to a digital copy of an original that has aged for several centuries, with its patina and its defects, necessarily leads to a collision between two very distinct historical moments, one medieval, the other contemporary. 

This unavoidable chronological telescoping has forced us to take decisions that may seem questionable. Since it is not possible to restore them to their original subtlety and precision, the surfaces of the scanned alabaster panels, now more or less heavily abraded, have not been subjected to any real retouching (with the exception of a slight smoothing). The obvious fractures and gaps, on the other hand, have been digitally repaired. Leaving these gaps would have led to embarrassing inconsistencies. The breaks would have created white areas that would have impaired the overall reading of the work. Without claiming to put ourselves in the place of the medieval sculptor, we therefore opted to fill in the gaps by digitally ‘resculpting’ the missing parts, in order to remain as close as possible to the coloured masses and their initial visual balance – since it is precisely these that we wanted to study and interpret.³¹

Despite the precautions and the care taken in the analyses and observations, not all uncertainties could be resolved. For example, the portable and non-invasive instruments used for in situ physico-chemical analyses are not (yet) as efficient as those installed in a laboratory and based on the study of paint samples taken from the panels. The use of micro-photography, limited to a magnification ratio of 1:1 (lens) or even 1:2 (extension ring), does not allow the detection of the smallest traces of polychromy. Other uncertainties are linked to the precise shade of a particular colour which is, in turn, due to natural variations in the hue of the pigments employed. For example, differences in the quality and origin of a mineral, such as azurite or cinnabar, or the fineness of the grinding process, generate variations in colour. Other pigments, such as red ochre, have a wide variety of shades ranging from deep brown through intense red to orange-red. Due to the gradual alteration of certain pigments over time, the colour shade visible today is often not the same as it was in the Middle Ages. Consequently, approximations cannot always be avoided. 

For our purposes, English alabasters nevertheless present a series of specificities that greatly facilitate the reconstruction of their polychromy, specificities to which we will return later in detail. The first of these is the very high number of artworks preserved. As English alabaster panels are remarkably homogeneous from a stylistic point of view, potential comparisons can be counted in the hundreds. These comparisons are all the more relevant as their painting follows a certain number of principles that apply to the whole of the production, or nearly so. This fact legitimises our attempts to fill in the gaps in the polychromy by relying on comparisons. Painters generally avoided mixing several colours and using half tones, preferring colours made up of a single pigment. This practice considerably restricts the pictorial palette and thus makes it easier to imitate it. The same holds true for the habit of the alabastermen of applying the colour in a covering and homogeneous manner, often creating monochrome flat tints: this avoidance of nuances and their giving up on modelling colours according to light and shade facilitate their reproduction. Given that these pictorial conventions were not those of an individual, but were shared and reproduced by a large number of painters for more than a century means that the conditions for reproducing them, even today, appear particularly favourable. 

Notes

1. Leaving aside the works of local 19th century scholars, most often related to the Bordeaux archbishop Pey Berland and his role as a commissioner of English alabasters, these include the following works: Brutails 1907, Le Noan-Vizioz 1957, Gardelles 1976, Gorguet 1984, Meunier 2003.
2. Hope 1890.
3. See Nelson 1914, idem 1915, idem 1917, etc.; Hildburgh 1916, idem 1917, idem 1918, etc.
4. Prior & Gardner 1912; Prior 1913.
5. Hildburgh 1946, idem 1955; Land 2011.
6. Cheetham 1984, reprint 2005; idem 2003; Dréan 1987; Gorguet 1984; Murat 2016.
7. De Beer 2018; Murat, ed. 2019.
8. Williamson, dir. 2010.
9. De Beer 2018; idem 2020.
10. Kloppmann et al. 2014; Kloppmann et al. 2018; see also the other contributions contained in vol. 200 of the Revue de l’art 2018.
11. Flavigny, 1997a (about the altarpiece of Saint Nicolas du Bosc/ Eure); Colinard & Klein 1997 (concerning the Rouvray altarpiece kept in the Musée départemental des Antiquités of Rouen).
12. Williamson, dir. 2010a.
13. Land 2011, 65-72.
14. De Beer 2018, in particular 115 (about the panels from Kettlebaston kept in the British Museum), 158-160 (about the Virgin and Child in the same museum) and 168-169 (about the Saint George slaying the dragon, National Gallery of Art in Washington). 
15. Murat, ed. 2019a; Brantley et al. 2020.
16. Woods 2020.
17. Colinard & Klein 1997.
18. Castro et al. 2008; Sarmiento et al. 2008.
19. Martiarena Lasa 2012 et idem 2013.
20. Pereira-Pardo et al. 2018.
21. Philipps & de Roemer 2019.
22. See the concept of paragone: Sauerländer 2002, 27-34. 
23. Fibre optic reflectance spectrometers (FORS).
24. The archaeometric results of the study on the polychromy of Aquitaine alabasters were presented in detail in Mounier et al. 2020. 
25. A spectrocolorimeter measures the chromaticity coordinates L*a*b*, where L* is the lightness (derived from the luminance of the surface) and a* and b* express the deviation of the colour from that of a grey surface of the same lightness. The L*a*b* coordinates were then converted to the RGB coordinates used by computer graphics software.
26. The experimental part (sculpture, painting, gilding) of the study on the polychromy of English alabasters kept in Aquitaine was presented in detail in Mulliez et al. 2022. 
27. For more details, see also Mulliez et al. 2022.
28. The scanner used is a HandySCAN 700 from Creaform.
29. The 3D model was obtained from 260 digital images, which were transformed into a point cloud using Photoscan software. This point cloud was then meshed: each point in the cloud is connected to the two closest points to create a triangular surface. The set of triangles thus created forms the surface of the virtual model. The 3D model is then transferred to a new chain of computer graphics software. The purpose of these is to simplify the model so that it can be manipulated on the computer. The decimation and retopology operations thus make it possible to reduce the number of triangles from several hundred million to a few million without significantly degrading the fidelity of the reproduction of volumes. The model is then textured using calibrated high-resolution photographs to restore its current appearance.
30. Developed at the Institut d’optique d’Aquitaine, this device, called the Coupole, combines a dome of 10 000 LEDs and a camera mounted on a robotic arm. The alabaster panel is placed under this dome. The LEDs make it possible to create a large number of different lighting situations, each of which is documented by means of a digital photograph. The data collected in this way is then processed by computer. For more details, see Mounier et al. 2020, 435-436 and 445.
31. The fact that alabaster panels very frequently reproduced the same scenes composed in the same way usually limits the risk of error for this type of virtual restoration.