Maarten van Heemskerck, Abraham and Isaac, sixteenth century. Oil on panel.

Panel paintings are especially sensitive to changes in humidity and temperature, which can cause warping or even structural cracks in the wood itself. Cracks in the painted surface can develop easily, since oil or tempera paint will not absorb the same amount of moisture as the wood and thus will expand at a different rate. Here, changes in the painting's microclimate over its life created cracks where wooden boards were joined together to make a larger panel. Numerous smaller cracks have also appeared in the painted surface.

The painting's structural problems likely developed early in its life, since old canvas-and-glue repairs survive on the panel's back to consolidate some cracking. Rather than endanger the panel's integrity by attempting to remove these, it was decided to leave them in place since they were stable and allowed the panel to function as a unit. However, lifting cleavages in the paint itself were carefully reattached to the surface over the course of several weeks. Old losses which had been painted over were cleaned and filled in with a uniform pigment as, for example, in the forearm of Isaac.