Barcol Hardness Tester

Originally named the Barber-Colman Impressor, the Barcol Hardness Tester was developed by Walter Colman during World War II as a portable device to evaluate the hardness of materials. The U.S. Air Force required a handheld method to check the hardness of rivets, as there were concerns that standard-quality rivets might be replaced with soft lead or wooden rivets, potentially compromising aircraft safety during flight.

The device operates by pressing its tip against the material under test. The depth of penetration of the indenter determines the material’s hardness. This is translated via a tension spring and lever mechanism to a reading on the dial.

The Barcol hardness test is commonly used on soft materials, such as rigid plastics. It measures hardness based on the depth of indentation made by a flat-tipped, sharp-pointed indenter. The method is similar to the Shore D hardness test, which also uses an indenter, though Shore D uses a rounded tip, while Barcol uses a pointed one. It should be noted that Barcol hardness is not suitable for sloped or curved surfaces.

When pressure is applied to the device, the pointed tip penetrates the material, and the hardness value is displayed on a dial graduated from 0 to 100.