Think like a detective. Establishing a timeline of events and providing evidence of a modus operandi associated with a particular criminal are key elements in police procedurals. These two types of tasks are also important activities in art historical scholarship. The chronology of the artworks produced by an artist is vital to the proper interpretation of an artist’s progress and impact. An understanding of an artist’s studio practice, including the preparation and use of particular materials, aids in the attribution of inadequately documented artworks.
In the study of old master paintings, one element to consider with regards to the artist’s materials is the canvas used as the painting’s support. During the 17th century in the Netherlands, canvas supplanted wood panels as the preferred material on which to paint. To prepare it for painting, the canvas was first coated with animal glue that reduced its absorbency. Then it was covered with a ground layer of paint to provide a smooth surface on which to construct the painting.
In the 17th century, shops in the Netherlands would buy rolls of canvas from weavers and sell them to artists in different formats. An artist could buy full or partial rolls of raw canvas that could be cut for individual paintings. The artist or artist’s assistants would mount these individual pieces on a strainer to keep their surfaces taut and then apply glue sizing and the ground layer. Shops also offered canvases in various dimensions already prepared with sizing and ground. In either case, the artist could use canvases that originally came from the same roll for multiple paintings.
Art investigators have generally presumed that two paintings in a similar style on canvas from the same roll were painted by the same artist—or by assistants in the artist’s studio. Since historical documentation supports the claim that
Until a decade ago, average thread count, measured separately in horizontal and vertical directions, was the preferred forensic attribute for making that determination. The typical number of threads per centimeter in each direction in Vermeer’s canvases ranges from around 10 to just over 20 (which corresponds to approximately 25 to 50 threads per inch). There are two limitations, however, in using average thread counts to identify pieces of canvas originally from the same roll. One is the time-consuming task of manually counting threads, which limits the number of spots that will be counted across the surface of the canvas, thereby weakening the accuracy of the data.
The vast majority of old master paintings have been relined to help mitigate the deterioration at the edges attached to the strainer. A new piece of canvas is glued to the back of the old canvas with the edges of the new canvas wrapped around and attached to the strainer. With paint covering the front of the painting, the original canvas is hidden. Because the ground layer typically includes paints such as lead white that attenuate x-rays, x-radiographs of paintings can be used to reveal the impressions of the threads in the ground layer. These impressions can be counted with suitable magnification of the x-radiographic image. The ground layer sitting atop each thread will be thinner than the amount that penetrates between the threads. This results in a variation in intensity of the x-ray that penetrates the canvas and is exposed on the film.
A more reliable and accurate approach for assessing the character of a canvas structure is to replace hand counting with computer algorithms. In 2007, the Thread Count Automation Project (TCAP) began using such algorithms to provide thread counts in square evaluation tiles across the entire surface of a painting.
For a timeline and other information regarding TCAP, see C. Richard Johnson Jr., “Thread Count Automation Project (TCAP) Timeline (2007–2014),” http://people.ece.cornell.edu/johnson/tcap.html.
A photographic or digital image analysis method that visually records an object's ability to absorb or transmit x-rays. The differential absorption pattern is useful for examining an object's internal structure as well as for comparing the variation in pigment types.
An explanation of this process and the software to implement it is provided in W. A. Sethares, “Automated Creation of Weave Maps,” in Counting Vermeer: Using Weave Maps to Study Vermeer’s Canvases, ed. C. R. Johnson Jr. (The Hague, 2017). This monograph is availble at countingvermeer.rkdmonographs.nl/ in conjunction with the exhibition Vermeer and the Masters of Genre Painting: Inspiration and Rivalry held at the National Gallery of Art from October 22, 2017, to January 21, 2018.
The vertical stripes in the weave map
In the intervening years since TCAP’s introduction in 2007, x-radiographs have been collected, with the assistance of the late Walter Liedtke, former curator of Dutch and Flemish paintings at the Metropolitan Museum of Art, providing full-painting images of 34 of Vermeer’s paintings.
Walter Liedtke, Vermeer: The Complete Paintings (Ghent, 2008).
The connected pairs are A Woman with a Lute and Woman Writing a Letter, with Her Maid (figs. 4 and 5), and Woman with a Pearl Necklace and Woman Holding a Balance (figs. 6 and 7). For further discussion of roll mates among Vermeer’s paintings, see C. R. Johnson Jr., “Exploiting Weave Maps,” in Counting Vermeer: Using Weave Maps to Study Vermeer’s Canvases, ed. C. R. Johnson Jr. (The Hague, 2017). This monograph is available at countingvermeer.rkdmonographs.nl/ in conjunction with the exhibition Vermeer and the Masters of Genre Painting: Inspiration and Rivalry held at the National Gallery of Art from October 22, 2017, to January 21, 2018.
C. Richard Johnson Jr.
Oct 19, 2017