
I first re-flattened the print by lightly misting the reverse with water to relax the paper and then drying it under weight. Once that was done, I mixed watercolors to match the colors of the print, testing them on a paper of similar color and texture. When I was satisfied with the color matches, I used a fine sable brush to dot the watercolor into the cracked areas until the white was no longer visible. After the paint dried, I inspected the results and touched it up slightly. When it was done, I showed it to my husband to see whether the damage and infill were obvious to fresh eyes; he wasn't sure until I pointed out where it was.
On the left is a detail of the print after treatment; the treated area is discernible on close examination (more so in person than in the photo), but it's no longer obvious and visually distracting. This was a fairly simple and brief project, but very satisfying.