I used the sepia ink both in Speedball steel nibbed pens and I watered it down to use like a watercolor. Wonderful stuff, it had a wide range of color depending upon saturation/amount, mixed fine with water, and lays down waterproof, wonderful for conjunction with watercolors. My new favorite ink.
I love love love these inks! Great, bright colors with high permanency ratings. Work well for painting opaquely but also create beautiful transparant washes.