The main culprit is usually not the ink itself but the paper: on absorbent copier paper inks like Private Reserve Tropical Blue spread more, while on better, sized paper (e.g. Clairefontaine) a clean line emerges. This is borne out: with better paper the bleed disappeared completely. Alternatively, the ink flow at the pen can be tuned by adjusting nib and feed alignment, although on expensive gold-nibbed pens many collectors do not feel comfortable doing this themselves. Big differences in ink viscosity are rarely observed in practice; brands like Diamine or Noodler's are not generally regarded as particularly "dry". When buying ink, an individual recommendation from experienced dealers like Rolf Thiel (missing-pen.de) is worthwhile.