Most organic materials and non-metallic materials who surfaces appear to be rough and highly absorbent, have an emissivity of essentially 0.98 or a nearly perfect emittance characteristic.  The materials cause few problems in making infrared temperature measurements.  When the emissivity is less than the perfect 1.0, the user must know how to set the emissivity in order to compensate for the less efficient emission characteristics.  The typical emissivities of known materials are presented in the Emissivity of Total Radiation for Various Metals Table.

The emissivity of a surface may be measured by comparison of the infrared thermometer reading with a standard contact thermometer on the same surface.  

A miniature, thin-film platinum resistance sensor is preferred for the contact sensor because it has a planar surface that makes better physical contact with the surface than a conventional probe.  A conventional probe may be used if modest error is acceptable.  Follow the manufacturer's recommendations for mounting any sensor to the test surface.  The contact sensor should be as small as possible and bare (unhoused), for best results.

Once the contact sensor is intimately attached to the Surface Under Test (SUT) and measuring properly, elevate thee temperature of the SUT and stabilize at a temperature near the upper end of the infrared thermometer’s span for approximately one hour for thick sections and proportionately less for thin sections.

After stabilization, aim the infrared thermometer at a spot on the SUT as close as possible to the contact sensor.  If your instrument has Visual Light Sighting, refocus the instrument until a ring configuration appears on the light spot.  Position the contact sensor in the dead center section of the ring.  Change the emissivity up or down until the infrared thermometer display reads the same as the contact thermometer following the instructions in the Operating Instructions.  The resulting emissivity reading is then equal to the emissivity of the SUT at that temperature and under those conditions.  Record this reading for future reference.

Another simple method of determining emissivity values of greybody surfaces up to approximately 400°C is to mask off a portion of the base surface with masking tape or scotch tape and pass the area adjoining the tape edge through a candle flame or “smoky” torch to deposit hydrocarbon soot on the area to effect a complete coverage.  This soot has a high, well defined emissivity of 0.955 ± 0.01, and has better thermal conductivity and a thinner section than paint so as not to affect the thermal balance of the substrate.  If the tape is now pulled off of the target, a sharp line will divide the soot-covered area from the bare area to be evaluated.

Heat the object to an appropriate temperature and, using an instrument with Light sighting with an emissivity setting of 0.95, measure the temperature of the soot area just adjacent to the bare material line.  Next, move the instrument over to where the light is just on the bare surface adjacent to the boundary and adjust the emissivity control to produce the same temperature reading that you got on the soot-covered area.  Record the value of this emissivity for future reference.