The K-55 Acrylic Paint Marker contain 30ml each of water-based opaque paint. The fluorescent colors glow under black light. Excellent for use on paper and painted surfaces, the 15mm block nib is best for smooth surfaces. A great marker for larger drawing, making signs and calligraphy. Handmade in the USA. Conforms to ASTM D-4236. Prop 65 compliant.