The Manufacturer and Builder 8, 1877
These pictures are nothing but a very ingenious application of the properties of the salts of nickel and cobalt, which become respectively green and red by being heated. In painting a winter scene, the trees, base, etc., are done in water-color; then the foliage is painted with a solution of the nickel salts, and the fruits on the trees, roses, and other red flowers are painted with the cobalt salts mentioned. When such a painting is cold, the latter are not seen, and the scene represents winter; when warmed before a fire the trees become green, and apples, roses, and red flowers appear, and it is a summer scene; when again exposed to cold (and especially to moisture) the green and red disappear, and it presents a winter scene again. This may be repeated an in-definite number of times.