Each swab is a self-contained test unit to provide a rapid specific test for lead. Will work on any surface, turning red or bright pink when lead is present. Each swab is ready to use. Sensitivity of 1 ug on solid surfaces, 2 ppm in liquid. There are no hidden steps or lengthy procedures. Odorless, disposable and non-staining with indefinite stability. The entire test procedure can be performed anywhere in 30 seconds. A test confirmation card is included to verify test results. EPA Recognized.