At the recent October Old Master auction at Dorotheum in Vienna, a Baptism of Christ, oil on panel, 75.5 x 107.5 cm, by Jacob de Backer (Antwerp c. 1555-1585/90) was presented as lot no. 18. The painting is dated to the 1580’s. 
On the back is a stamp with what looks like an encircled St. Andrew’s cross with an additional horizontal crossbar. This mark, measuring about 20 mm across, is rarely found on panels and we only know of a few examples. One is on a painting depicting Our Lady in the Carmelite Convent in Sens (Yonne), and the other on a panel (reused more than a century after its fabrication) now kept in the National Museum in Gdańsk.
At current, we have no firm evidence of who of the many Antwerp panel makers was using this particular design for his stamp. However, on the list from 1617 the house-mark next to the name of Hans Van Haecht is drawn as a triple cross. Hans Van Haecht came out of a large dynasty of painters, panel makers, carpenters and art dealers. Although he is mostly known as an art dealer bills concerning deliverance of panels are known as well. He was active as a panel maker in Antwerp 1589-1621.
Further, we know of several seemingly identical marks to the one on De Backer’s panel, but they are all only half the size and appear on apparently later panels (?). Additionally we in at least two cases have observed the triple-cross written in red chalk on the back of panels.
More on all this on a forthcoming occasion …
 Luuk Pijl and Nils Büttner has individually confirmed the attribution, provenance and dating of the present painting.
 M. Schuster-Gawłowska, ‘Guild Marks on the Backs of Flemish Panel Paintings. An Attempt at Systematization and Documentation’, in Studia i Materiały wydziału konserwacji dzieł sztuki Akademii sztuk pięknych w Krakowie, Tom II, 1992, pp. 64-65.
 Jan Van Damme, ‘De Antwerpse tafereelmakers en hun merken. Identificatie en betekenis’, in Jaarboek voor het Koninklijk Museum voor Schone Kunsten, Antwerpen 1990, p. 195.
 J. Van Roey, ‘Het Antwerpse geslacht Van Haecht (Verhaecht). Tafereelmakers, Schilders, Kunsthandelaers’, in Miscellanea Josef Duverger, vol. I, Gent 1968, p. 216-230.