Flat-black paint was used on all solar collectors up to the late 1970s. Although this coating has high absorption (about 95% of solar radiation), it also has high emissivity (also about 95%), resulting in efficiency losses.
A significant improvement in collector performance came from the advent of selective-surface coatings, which absorb about as much radiation as flat-black paint but emit only 10% to 20%. This amounts to a gain of a few percentage points in collector performance. A selective coating is a complex and expensive process compared to simply painting an absorber—but it is worthwhile in many cases, such as installations in colder climates. Some selective-surface coatings are called black chrome, black crystal, and sputtered aluminum.