PITT Artist Pens are acid-free, water-based pigment ink that is rich with high quality pigments. The colors are transparent and can be layered to create your own color. The acid-free water-based pigment ink is made with pure pigment that has a high level of color and transparency, smear-proof and non-bleeding. The colors will stay vibrant for a long time. Once adhered to the paper, it will not bleed through or bleed through. Great for use with other art supplies such as watercolor pencils. Ink pens are often used by artists as well as graphic designers. High quality nibs allow you to move the brush in any direction without bending over. Darker colors can also be used to fill the bottom color beautifully. The degree of lightfastness is indicated with a star mark on the body.