Kreuzigungsaltar: Apostel Philippus, Matthäus und Jacobus d. J. Rückseite: Hl. Christophorus (mit Stefan Lochner)

The Kreuzigungsaltar panel with Apostles Philip, Matthew, and James the Younger on one side and Saint Christopher on the reverse was painted by the Master of the Heisterbach Altar in collaboration with Stefan Lochner, the most celebrated Cologne painter of the 15th century. This collaboration — documented through stylistic analysis rather than archival evidence — places the panel at the center of Cologne's early 15th-century workshop culture, in which artists shared commissions and visual ideas before the guild system fully regulated such arrangements. Lochner's sweetly lyrical figure style and the Heisterbach Master's more angular approach are distinguishable within the same altarpiece program.

The composite authorship creates a stylistic tension visible in the panel: the Heisterbach Master's figures tend toward firmer contour and more architectural spatial organization, while sections attributable to Lochner's workshop show the soft golden tonality and tender facial expression characteristic of his Virgin paintings.