Pen with phosphorous ink for easy marking of those membranes ready for exposure. The fine tip of the pen also allows individual bands and gel tracks to be marked simply and easily. Directions for use The marking is activated by the light in the room prior to exposure. The ink illuminates the X-ray film during exposure and the letters are visible in black ink. The letters are easy to read even after short exposure time. In the event of long exposure, the short half-life value of 2-3 minutes effectively prevents overexposure. The writing is therefore easy to make out after virtually all exposure times. Through the replacement nibs the pen can be reused even after a number of months or after drying out. Suitable for chemoluminescence and isotope-radiography. Ideal for marking paper, plastic foil and dried polyacrylamide gels. Autoradiography Pen Delivery incl. 1 pen + 4 replacement nibs