a method and system for assessing proper pre - processing and proper welding of polymer workpieces . a visible or infrared radiation source , optionally coupled with optical filters , directs radiation at test wavelengths through a workpiece which is captured by sensors at one or more stations . the system controller determines from the sensor data whether the absorber dye was properly deposited onto the workpiece . the workpiece is then certified weld - enabled within a bandwidth range of the test wavelength . the bandwidth range is determined by absorption spectra and extinction coefficients of the dye or by utilizing multiple test wavelengths . for determining whether proper welds occurred , a further embodiment of the method and system check for spectral characteristics that the dye vehicle did not unduly interfere or occlude the weld . further spectral data indicates fusing of reflective surfaces , increased transmission and increase photopic transmission .