Formulated, tested, and approved. For marking on painted steel, iron, glass, aluminum, and other materials. Will resist rain, sunlight, and other harsh outdoor conditions. Instant drying. Water-based. Xylene-free. Acid-free. Non-hazardous. Pigmented paint. Leaves no residue. Removable With Windex and other ammonia-based wet-wipe products. Keep pen from freezing.