Just like the classic PX-30 & PX-20, the UNI PX-21 is quality Xylene-oil based, with extreme weather resistance and a gloss finish on non-porous surfaces. Excellent coverage on a number of surfaces from metal to paper. Because these are oil based they do bleed on soft papers, and it is highly recommended to whip the inside of the cap and rim of the nib after use. Excellent weather resistance, opaque color. Small point nib.