Although halos can be found in a substantial number of 17th-century Dutch and Flemish paintings, the topic has so far received little attention in technical literature. Paintings conservator Martin Bijl reported a halo in Steen’s The ill woman (Fig. 3B) in a 1996 exhibition catalogue , describing it as a characteristic element of Steen’s painting style of the late 1650s. In view of the aforementioned occurrences in the oeuvre of different artists working in different painting styles and genres, it is now clear that the dark halo technique cannot be regarded as part of an artist’s personal painting style. On the contrary, this albeit understudied technique seems rather an established element in the genesis of a 17th-century composition.
In a 1996 paper, Jørgen Wadum mentioned corrections in paintings by Rubens, executed in a dark material and with broad brushstrokes . With IRR, dark outlines along the contours of the figures were detected (see Fig. 7A–E). Wadum interpreted these broad brushstrokes as corrections to the figures; it is known that Rubens inspected and corrected the paintings before they left his studio. However, this hypothesis was refuted by Nico Van Hout in his doctoral dissertation. It seems unlikely that dark halos are corrections, as it seems that there is no paint layer present underneath this dark paint. Additionally, the dark halos were applied in the underpainting stage. According to Van Hout, making such bold corrections in the underpainting stage seems rather unnecessary and not very typical of Rubens .
In the aforementioned 20th National Gallery Technical Bulletin (1999), Roy suggested that Van Dyck employed halos as an aid to define the exact placement of the figures in the composition during the underdrawing stage. Along with the double portrait in Fig. 5, Roy adds The Abbé Scaglia adoring Virgin and Child and Portrait of the Abbé Scaglia as examples (see Fig. 7F–H) . This hypothesis does not clarify in a satisfactory way why the artist would have abandoned the established and more efficient practice of (slimmer) markings in a dry and/or wet medium for these purposes, which are easier to cover up. As attested by Sweerts Peasant Family, the halo might require additional efforts in the final stages of the painting process to mask or diminish its impact on the eventual visual appearance of the painting.
Nico Van Hout , on the other hand, argues that Rubens would have turned this potential optical effect to the better, by proposing that the artist would have incorporated the halos consciously to emphasize certain elements (e.g. hands) in the composition. By using these dark halos, Rubens would have been able to indicate areas that were supposed to be underpainted and clearly distinguish them from areas where the imprimatura needed to play an visual role [18, 19]. In addition, by placing darker tones directly adjacent to lighter areas such as flesh tones, the sense of depth was enhanced in the composition. This line of reasoning was underpinned by Van der Snickt et al. in , discussing the MA-XRF results on the aforementioned Incredulity of Saint Thomas (see Fig. 8). By placing a dark halo around Thomas’ hand, Rubens might have wanted to draw the eye of the viewer to the hand that plays an important role in the biblical story. This double function makes sense in the context of Rubens’ efficient brushwork, where he wanted to achieve an optical effect that works best when experienced from a distance; however, it remains unclear to what extent the halo was visible at the surface of the painting at the time of its creation, considering the aforementioned tendency of oil paint to become more transparent over time. In addition, this theory does not entirely stand up for works by Rubens that currently exhibit halos. For instance, it seems unlikely that in Venus Frigida, the halos around the backside of Amor and around Venus’ foot were applied to draw the attention to these parts, since they lack iconographical importance (Fig. 9). Also, the tonality of the surrounding surface paint already appears to provide for the necessary contrast. Bearing in mind the prevalence of the halos in many other oeuvres, it seems more likely that Rubens had a different motivation for working with these subtle pictorial elements. Interestingly, Rubens’ early works of the 1610s are the earliest examples of the halo technique reported so far. As such, the question arises if the highly influential artist with his many assistants and students, and an intellectual spill-over was the artist who introduced, or at least disseminated the dark halo technique in Flemish and Dutch Baroque painting . If this is the case, the question remains whether he (or any other resourceful colleague) picked up this practice during his time in Italy upon studying the work of contemporary or preceding colleagues, or if he developed this approach himself.
Ella Hendriks supplied the most plausible theory when discussing the working methods of Johannes Cornelisz. Verspronck. She rationalized the technique as a way to provide a “foil against which the tones of the portrait could be established” . With this dark halo applied along the contours of the face of the sitter, an artist could establish the correct highlights, midtones and shadow tones right away. We would like to build on Hendriks’ hypothesis: we argue that the halo serves as a color reference in the earliest painting stage, when no tonal benchmark was available to the artist .
The latter principle is probably best grasped when looking at David’s unfinished Oath at the Tennis Court in Fig. 2C. This notion might also justify the emergence of halos in 17th-century painting, and not earlier, in 15th- or 16th-century painting. This because the 17th-century way of painting was different from the methods used by earlier artists. 15th- and 16th-century artists typically worked from background to foreground, leaving reserves in anticipation of the main figures that were painted later. With this approach, artists applied plenty of colors to hold on to from the beginning: they had a tonal benchmark when painting the main figures. This tradition is abandoned in the seventeenth century, when artists reversed the working sequence: they may have started by painting the main figures, while later adding the background. Artists did not have a tonal benchmark when painting the main figures according to this painting method: the dark halo could serve as such a tonal benchmark. In this viewpoint, dark halos are also in line with the efficient studio practice of that era, as the sitter could approve the portrait prior to investing work in the rest of the painting. In addition, the halo indicated the final tonality of the background, which would allow a studio assistant to finish the remaining parts independently. This may definitely be the case for artists like Rubens, who was known for having a lot of assistants and students. However, not every artist had assistants. Michael Sweerts for instance, whose work is discussed below as a case study, is known to only have had one student throughout his career. The records of the Brussels painter’s guild only mention Jean-Baptist Borremans, who was registered as an apprentice of Sweerts in 1657. No other assistants, students or apprentices are mentioned in the records of the guild . It remains unknown whether Sweerts had an assistant or apprentice while working in Italy. The 17th-century also marks the period in which Dutch and Flemish artists transitioned from working on white or off-white grounds to (strongly) colored grounds . Such a colored ground, ranging from (dark) grey, to brown and even red, could function as a midtone for the composition.
At the same time, a dark halo in the underpainting might serve a second, different function, which is specifically related to portrait painting. When painting a portrait, artists need to pay attention to so-called hard and soft lines. The outer contours of a face need to softly blend into the background in order to create three dimensionality and liveliness. To be able to achieve such a soft blend, it is necessary to add a (dark) halo around the face of the sitter. This means that a dark halo along the face of a sitter may not have only served as a color reference, but also helped the artist to achieve a naturalistic portrait, with convincing modelling and three dimensionality.