Only in a few places, such as the beard and hat, can we easily discern the broad lines typical of many parts of the central panel. They differ from the fine lines of a mouth apparently originally planned to be closed and the hatching of the left-hand point of the collar, which may be part of a second stage in the underdrawing, carried out to define the forms more closely. These lines, which suggest a dry medium, could indicate the use of a number of different drawing mediums not all of which can be revealed by the infrared. This supposition is also supported by the fact that colour abbreviation resembling a reversed figure ‘4’ is to be found on the collar worn by this figure, but nowhere else on the altarpiece (see red mapping lines). This symbol is familiar, for after all it is one of the set of seven different signs hitherto attested in the underdrawings of a number of paintings by Stefan Lochner and the Master of the Heisterbach Altarpiece. Signs of this kind indicate the planned coloration of garments, so as a rule they can be found several times in the same work.
Not in the underdrawing, but certainly in the painting, we see on the grey surface of the hat, in illusory relief, two signs that at first sight look like the letter ‘S’ (see red mapping lines). In fact only the sign on the left is an ‘S’, the other is almost certainly a ‘Y’. In view of the first letter, the first idea that comes to mind is that it stands for Lochner’s first name Stefan, and could therefore be a hidden signature; however, in view of the second letter, this seems not altogether plausible. How, though, are the senile warts to be interpreted, which represent a distinguishing feature of the person depicted? According to Tobias Burg, this is not likely to be a self-portrayal of the artist as an ancillary figure because (a) the figure plays a coherent part in the composition, as a counterpart to the figure of the young Magus on the right; (b) there is no inscription that can be unambiguously decrypted or interpreted as a signature; (c) there was no tradition of doing this in the German-speaking area at the time; and (d) the person in question is not looking out of the picture, which while not a clinching detail, might have been expected. On the other hand, Burg notes that the figure in question does stand out clearly from the action in the rest of the picture. Given the less schematized, and as a result of the warts additionally individualized face, and not least in view of the unique letters on the hat (which contemporaries might have been able to decipher), he thinks it possible that a real person is depicted here. Interestingly, Burg thinks the figure in question is even less likely to be a portrait of a donor (another conceivable possibility) than of the artist himself.
(With thanks to Clemens M.M. Bayer for identifying the letters, and to Dr Tobias Burg for his expert opinion regarding the possible self-portrayal of Stefan Lochner.)