Abstract: A method for detecting and measuring regions of a secondary material deposited onto a moving substrate. The method employs an x-ray source for directing an x-ray beam at the moving substrate, and an x-ray detector to detect an amount of x-ray energy transmitted by the moving sheet of material. Areas of bare substrate will allow for different amounts of x-ray transmission than areas of the substrate containing the secondary material. These differences in transmission and/or absorption can be used to detect the location of a region of secondary material and to determine if it falls within an acceptable range. According to one particular embodiment of the present invention, the method can be used to analyze burn characteristic modifying bands of a secondary material intermittently and repeatedly deposited to a moving web of smoking article paper.