This test is performed by first pyrolyzing the rubber under a high vacuum in the absence of oxygen. This removes all of the rubber, oils and other volatile compound additives and leaves the ash and carbon black behind. If a large amount of inorganic filler such as silica or calcium carbonate is present, the ash/black blend can then be treated with different acids to further isolate the carbon black.

The sample is then dispersed and placed on a copper grid coated with a very thin layer of evaporated carbon to be analyzed in the transmission electron microscope (TEM). Photomicrographs of the carbon black agglomerates are then taken with the TEM and transferred to a computer.

The primary particle size of individual carbon black particles within the agglomerates are then measured using calibrated computer software. The average particle size and distribution is then analyzed and compared to known standards. A determination of general carbon black type is then made based on this comparison and reported as a general type of carbon black (N100, N200, etc.). In many cases it can also be determined if a blend of carbon blacks are present.