KWZ IG Turquoise ink reviewed by Skribr. KWZ Iron gall inks have higher resistance to water and fading than regular fountain pen inks as they contain small portions of metal particles. These particles are derived from iron and oxidize when exposed to atmosphere and darken as the ink dries on the paper. Skribr performs a water resistance test to see how the ink reacts to liquid. Tested with a TWSBI ECO fountain pen and Rhodia paper.