RKD STUDIES

Interpretation of an artist’s painting technique from an X-radiographic image requires careful comparison with the painting and a thorough knowledge of the artist’s materials. The following section looks at the different aspects of Vermeer’s painting technique that can be determined from X-radiographs.

2.5.1 Painting supports and format
Since Vermeer’s ground layers contain lead white, the study of X-radiographs provides much information about the characteristics and condition of the supports. For his paintings on canvas, features visible in the X-ray include thread thickness, thread density (thread count), type of weave, as well as the presence of weave faults from hand-operated looms (such as double or triple threads or so-called weft-snakes, see chapter 6), selvedges, seams, and deformations along the edges due to stretching of the canvas support, known as cusping. These features are important to study and compare when paintings are suspected of being pendants or possible roll mates (see chapter 6 for other examples).¹ The study of X-radiographs can also provide insight about a painting’s original size, as well as information about the original strainer and the way the painting was mounted onto the strainer, in addition to features relating to past interventions and damages, such as additions, inserts, repairs, folds, tears, holes and even if the painting has been transferred from another support in the past. For panel paintings usually the type of wood can be discerned, along with the direction of the wood grain, as well as the presence of joins, losses, woodworm infestation, cracks, auxilliary supports and old repairs. The visualization of the wood grain or canvas weave is related to the type of ground that is in contact with the support. It is the penetration of the ground between the canvas threads or the grain of the wood that allows the structure of the support to be imaged in a X-ray. In paintings where no radio-absorbent pigment is present in the ground, the structure of the support will be difficult to see in a X-radiograph.

Different kinds of fabrics made from both linen and hemp were available to artists as canvas supports (see chapter 3). The fibers cannot be identified in an X-radiograph; instead polarized light microscopy is used. Tabby or plain weave is the most common type of weave encountered in seventeenth-century Dutch paintings. It is notable that Vermeer painted on plain weave canvas that is remarkably regular and of high quality compared to the canvas supports of many other seventeenth-century Dutch artists, including Rembrandt, whose canvases show many irregularities in thread thickness [1].

The majority of Vermeer’s paintings are painted on canvas. Only two (small) paintings are on oak panel (Girl with the Red Hat (L24) and Girl with a Flute (L25)). In the case of The Little Street (L11) the canvas fiber has been identified as linen.² Due to the way canvas was stretched and prepared in the seventeenth century, deformations, known as cusping, can occur along the edges (see chapter 3). In the past close inspection of the X-ray using a head magnifier was needed to accurately measure and characterize such deformations, but with the recent development of digital methods, cusping can now easily be discerned in so-called ‘thread angle maps’ (see chapters 5 and 6). In many cases the presence, or absence, of cusping along the margins can help in the determination of the original format of a painting. For View of Delft (L12) cusping is visible in the X-ray on all four sides indicating (along with the unpainted, original tacking edges) that the format of the painting is unchanged. That is not the case, however for Diana and Her Nymphs (L01), where the X-radiograph revealed the absence of cusping on the right edge of the picture suggesting the canvas support may have been cut down. This was confirmed during the 1999-2000 treatment of the painting, when the old lining canvas was removed, revealing an imprint of the presumably original seventeenth-century strainer in a paint layer on the reverse of the original canvas. Comparison of the partial imprint of the corner bar of the strainer in the upper right, with the imprint of the complete corner bar in the upper left, indicated a reduction of some 12 cm had occurred on the right side of the painting. Importantly this meant that the painting was originally the same size as View of Delft (L12).³

Information about the original strainers, and in some cases even the original method of mounting the canvas to the strainer, is often also visible in X-radiographs. Lines of cracks parallel to the edges of a painting, caused by the original strainer bars, can frequently be discerned in X-radiographs [2a, 2b]. This type of crack pattern, often referred to as ‘strainer bar cracks’, gives information on the type and size of seventeenth century strainers, which are rarely preserved. An exception is Vermeer’s The Guitar Player (L35) that has retained its original four-member strainer with bars that vary from 2.1 to 2.7 cm in width [2c].⁴ The ‘strainer bar cracks’ present in The Milkmaid (L07), Woman in Reading a Letter (L17), Woman with a Pearl Necklace (L18) and Woman Holding a Balance (L19) indicate similar strainers were used in these relatively small pictures, which are all comparable in size with The Guitar Player (L35). In Vermeer’s larger paintings such as the just mentioned Diana and Her Nymphs (L01), View of Delft (L12) and The Art of Painting (L26), the ‘strainer bar cracks’ in the corners of the X-rays indicate these (larger) paintings originally had strainers reinforced with corner bars.⁵

1
Irregularities in thread thickness is characteristic of hand-spun fibers of canvas. Weave faults from hand-operated looms used in the seventeenth century are usually also present.
On the left is a detail of the X-radiograph of Vermeer’s Woman Writing a Letter with Her Maid showing the regular nature of the canvas. The detail of the X-radiograph on the right showing knots and variations in thread thickness is from Rembrandt’s Still Life with Peacocks, c. 1639 (Rijksmuseum, Amsterdam).

2a
X-ray of The Guitar Player

2.5.2 Grounds

Recent study of Vermeer’s ground layers indicates they are more similar than previously thought.⁶ The majority of his grounds are composed of one or two layers of light or dark beige paint containing lead white, with the admixture of chalk, earth pigments and fine black, as well as a little umber. Due to the presence of lead white, the grounds are strongly visible in the X-radiographs. This is not always the case. For instance, Rembrandt’s quartz-rich grounds hardly register at all in X-radiographs [4]. X-rays can also provide evidence of how the ground layer was applied. For instance, in The Little Street (L11), the X-radiograph provides evidence that the ground was applied in large curved movements with a priming knife. The movements of the priming knife can be deduced from curved thicker ridges of ground that show up lighter in the X-radiograph (see arrows in [3]).

2.5.3 Pigments and paint layer build-up

The presence of lead white in the paint layers of Vermeer paintings (in addition to the ground layers) also means that X-radiographs are particularly useful in the study of the paint layers. In addition to lead white, other pigments, such as lead-tin yellow, frequently used for highlights, and the bright red pigment vermilion used by Vermeer for details such as ribbons and bows, also absorb X-rays and look whitish in X-radiographs. Organic pigments, earth pigments, copper-based pigments and blacks are transparent to X-rays to varying degrees, and depending on admixtures with other pigments appear medium to dark in an X-radiograph. Due to their differences in radio-absorbency certain red and yellow pigments can be distinguished from each other: red and yellow earths will appear dark in an X-ray, while vermilion and lead-tin yellow will appear light. It is therefore important to keep in mind that only a limited range of pigments register in an X-ray.

X-radiographs reveal several interesting features of Vermeer’s painting technique, such as the distribution of light and shade, use of reserves – areas in a painting which were left empty (in reserve), so that a planned feature could be added later – and his characteristic use of underpaints. The lead-white underpaint for instance, below the blue sky in The Little Street (L11) absorbs X-rays and therefore shows up white in the X-radiograph. For the most part, the houses were left in reserve in this lead-white underlayer and therefore register dark in the X-ray. This explains the strong contrast in the X-ray and is characteristic of how Vermeer established areas of light and dark in the early stages of the painting process [3]. This is also the case in View of Delft (L12) and tells us something about the order of painting. The townscape, which was left in reserve in the lead-white underlayer of the sky, was first laid in with a dark sketch or underpaint. This explains the strong contrast in the X-ray and is characteristic of how Vermeer established areas of light and dark in the early stages of the painting process [5a, 5b]. Certain details of the buildings, such as the chimney at the far left, however, were not left in reserve, but instead were added later over the sky and explains why they are not visible in the X-ray [5c, 5d].

Girl with a Pearl Earring (L22) also has a dark sketch or underpaint that consists of radio-transparent pigments and varies in tone and thickness. In dark areas of the figure, the underpaint is thicker and consists of bone black and some brown ochre, while in the lighter areas a thinner layer was applied containing yellow, brown and a little red ochre with a small addition of charcoal black.⁷ On top of this, the figure was worked up in just one or two paint layers, in some places such as the shadows of the yellow jacket, leaving the dark underlayer to shimmer through. The thick application of lead-white containing flesh paint in the lit areas of the face of the girl explains the strong contrast observed between the light and dark areas of the face in the X-radiograph, a contrast that the painting itself does not display [6].

As previously discussed (see §2.3), the strong contrast was one of the arguments used in the Van Meegeren trial to distinguish Van Meegeren’s forgeries from authentic Vermeer paintings.

X-radiographs also reveal the expressive brushwork of Vermeer’s underpaints, a feature of Vermeer’s painting technique that was already pointed out by Burroughs in his 1938 publication. Given the smooth modelling of the final paint layers this is somewhat surprising, and can be discerned for instance, in the underpaint of the wall at the left and right of the woman in the X-radiograph of Vermeer’s Woman Reading a Letter (L17). In this painting, the lively brushwork originates from the lead-white containing pale yellow underpaint, which partially shows through the thin, smooth, light blue upper paint layer of the wall [7a, 7b]. The combination of a textured underpaint, with a smooth top paint layer is considered a characteristic feature of Vermeer’s painting technique.⁸ The underpaint in the foreground of View of Delft (L12) also displays expressive brushwork. The broad diagonal brushstrokes of the lead-white containing underpaint are clearly visible in the X-ray image and shimmer through the smooth yellowish rose-colored surface paint [7c, 7d].

6
Detail of the X-ray of Girl with a Pearl Earring. The paint build-up and type of pigments used for painting the face have resulted in a strong contrast between the lit and shadow areas of the girl’s face in the X-radiograph, a characteristic feature of Vermeer’s painting technique that is less visible in the painting itself.

2.5.4 Compositional changes

The study of X-radiographs also provides exceptional insight into the way Vermeer developed his compositions. In contrast to what is suggested by the serene atmosphere, the compositions of the majority of Vermeer’s paintings were not established right from the beginning. Rather Vermeer carefully constructed his compositions during the painting process by changing, adding and removing elements. While these changes are not always visible with the naked eye, they can be revealed by careful study of X-radiographs. When such changes become visible to the naked eye they are often referred to as ‘pentimenti’.

The many small adjustments in the size or positioning of the different elements can be found in nearly all Vermeer’s paintings and provide evidence of his creative process. For instance in View of Delft (L12), Vermeer enlarged the reflection of the twin towers of the Rotterdam Gate in the water, extending the shadow all the way to the bottom edge of the painting [8a, 8b]. Initially Vermeer also included another man to the right of the two women in the foreground, but later painted him out.

In the carefully composed Young Woman with a Water Pitcher (L13), the map was originally placed behind the head of the woman and was later shifted to the right, an intervention that sets the woman off against the light surface of the wall. Likewise in Woman Reading a Letter (L17), the X-ray reveals that Vermeer extended the map some 3 cm to the left over the background paint. This is visible in the X-ray as a light band due to the X-ray absorption of the extra paint layer [9a, 9b]. That Vermeer initially left a reserve for the map in the lead-white containing paint of the wall is evident from the dark rectangle behind the woman in the X-ray. The X-radiograph also reveals that Vermeer altered the initially flared shape of the woman’s jacket (the original reserve of the jacket in the background paint is visible in the X-ray as a slightly darker shape). This revision serves to unify and reinforce the areas of the white wall to the left and right of the woman and create a more harmonious and balanced composition. The white shape along the bottom of the jacket also suggests the painter initially planned a fur trim that was left out in the final paint [10a, 10b].

In addition to these subtle compositional refinements, Vermeer also made more significant changes to his compositions by removing or adding elements. For instance, in the above mentioned Young Woman with a Water Pitcher (L13), a chair with lion-head finials originally in the left foreground, was entirely painted out. This simplified the composition by framing the woman with larger areas of white wall. In the X-ray of the Woman with a Pearl Necklace (L18) a map on the rear wall was added behind the woman and more of the floor tiles were visible than we now see in the final painting.

Sometimes these changes even have iconographic implications. In the X-radiograph of A Maid Asleep (L04), Vermeer initially planned a standing figure with a wide brimmed hat in the background room with a dog looking at him from the doorway. The head of the man was later painted over with a mirror in the final version, and the dog with a chair in the lower right corner. Wheelock argued that by leaving out these narrative elements, the viewer is left with no clear explanation for the woman’s mood, showing Vermeer was searching for a poetic approach to his subject matter rather than for an explicit narrative.⁹ Also a vague rectangular shape in the background of the X-radiograph of The Milkmaid (L07), shows Vermeer painted out a shelf or mantelpiece on the back wall and replaced a clothesbasket in the lower right with a foot warmer. These changes can have iconographic implications. In this case, the foot warmer can be associated with desire, and relates to the images of cupids on the row of tiles behind.¹⁰

Surprisingly, no changes can be observed in theX-ray of the large and complex The Art of Painting (L26) from 1666-1668. This would seem to suggest, that for this painting, Vermeer worked out his composition beforehand.¹¹ The absence of changes in other large works, such as Diana and her Nymphs (L01) and Christ in the House of Martha and Mary (L02) is also notable, although for these early paintings, works by other artists may have served as examples and therefore can explain the absence of compositional changes.¹² That Vermeer worked-out the composition beforehand or looked to other examples is certainly not the case for all large works. This is evident from the compositional changes visible in the X-radiograph of The Procuress (L03) or the earlier described changes in View of Delft (L12).

2.5.5 Optical devices, pinholes and perspective lines

Whether or not the artist made use of the camera obscura, is a much debated topic.¹³ Vermeer’s paintings indeed display many characteristics that can be associated with the use of optical devices: the artist’s accentuated contrasts of light and dark, the sometimes blurred or distorted depiction of objects that are close-by, the soft focus contours and his characteristic ‘diffuse highlights and light accents’. Also, the strong contrast in scale between foreground objects and those further removed from the picture plane, and the tight cropping of his compositions – as is common in photography – are features that could be attributed to the use of the camera obscura to aid the painter in framing his compositions.¹⁴

While the camera obscura may have been used as a compositional aid and be responsible for many of the visual effects in Vermeer’s paintings, pinholes found at the vanishing points of some seventeen of his paintings – as visible in X-radiographs – demonstrate that the artist used a mechanical procedure to construct perspective lines in his compositions. First observed in 1949 by Karl Hultén in The Art of Painting (L26), Jørgen Wadum went on to show how the artist constructed the orthogonals of the tiles or furniture by placing a pin in the canvas at the vanishing point to which he attached a cord covered in chalk. By pulling the cord taut against the canvas the chalk would leave a thin line.¹⁵

This practical technique, still used by artists and interior decorators today, was well established, as pinholes have since been observed in numerous works by many artists, amongst others Hans (1527-circa 1607) and Paul Vredeman de Vries (1567-1617), Thomas de Keyser (1596-1667), Gerard Houckgeest (circa 1600-1661), Jan van der Vucht (1603-1637), Anthonie de Lorme (1610-1637), Ludolf de Jongh (1616-1679), Emanuel de Witte (1617-1692), Cornelis de Man (1621-1706), Pieter Janssens Elinga (1623-1682), Hendrick van der Burch (circa 1625-after 1664), and Pieter de Hooch (1629-1684).¹⁶ Remarkable evidence of this method is found in a panel by Dirck van Delen (1605-1671), Iconoclasm in a Church (1630) in the Rijksmuseum where part of the metal pin onto which the piece of string would have been attached is still present in the painting [11].

To date pinholes have been discovered at the vanishing point in seventeen paintings by Vermeer.¹⁷ In most cases the pinholes are difficult to discern on the paint surface with the unaided eye. In Vermeer’s The Art of Painting (L26) the pinhole is apparent in the paint surface just underneath the tassel of the map, near Clio’s hand. Pinholes can be more easily detected in X-radiographs where they mostly appear as dark spots, where the lead-white containing ground was lost when the pin was inserted into the painting. In Woman at the Virginal with a Gentleman (L15), the central vanishing point is positioned in the left arm of the woman at the virginal and appears as a dark spot in the X-radiograph [12]. They can also appear as white spots in X-rays when the holes have been subsequently filled with a radio-absorbent paint. This is seen for instance in Woman Holding a Balance (L19) [13].

Small holes located at the outer edges of paintings can also indicate a second vanishing point. This is possibly the case in the early The Glass of Wine (L08), where close examination of the X-radiograph shows a small damage at the right outer edge which seems to indicate the vanishing point for the window.¹⁸ In the case of The Art of Painting (L26), a small hole at the outer right edge of the picture indicates the vanishing point of the chair on which the painter in the picture is seated.¹⁹ This vanishing point (as well as that of the central vanishing point) appears as a black dot in the X-radiograph.

11
Detail of Dirck van Delen, Iconoclasm in a Church, 1630 (Rijksmuseum). Remains of a pin are still preserved at the vanishing point in the panel.

12
Left detail of Woman at the Virginal with a Gentleman showing the pinhole (dark spot in white circle), and right, corresponding detail in the X-ray, showing the pinhole as a black spot where the radio-absorbent ground is missing.

13
Left detail of Woman Holding a Balance showing the small pinhole, and right, the same detail in the X-ray where the hole was subsequently filled with radio-absorbent paint.