Properly Calibrating an Infrared Thermometer
Infrared thermometers can be calibrated for accuracy just like other thermometers. In calibration labs (like the NIST-Traceable ThermoWorks Calibration Laboratory in American Fork, Utah), technicians use industrial black bodies (like the IR-500 Portable IR Calibrator) to calibrate infrared thermometers.
Black bodies approximate zero reflected ambient radiation and therefore the unimpeded emission of infrared energy for a given emissivity value (typically 0.95). Short of using a black body, the next best way to calibrate your infrared thermometer is to use a simple, inexpensive Infrared Comparator Cup. It is best to calibrate your infrared thermometer at more than one temperature (at 41°F [5°C] and 140°F [60°C] for example) and the Infrared Comparator Cup makes it easy.
If neither an industrial black body or a comparator cup are available, however, you can do a quick calibration using a properly made ice bath.
The usual challenges of using a boiling point for calibration (having to factor in air pressure and elevation) are further complicated with infrared thermometers because of the steam generated by boiling. Steam and the evaporative cooling and condensation that accompany it make it very difficult to get an accurate infrared measurement of a boiling liquid. But the surface of a properly made ice bath is reliably 32.0°F (0.0°C).