Graf von Faber-Castell was founded in 1761 and developed into the major manufacturer of wood-cased pencils. With time they started to offer much broader range of products. Few years ago company's introduced six inks. Last year they've added three new colors to the line. This year they've done the same. Three new GvFC colors hit the shelves.
Viper Green is quite nice. It's not the most saturated green ink ever created but it remains perfectly legible in all conditions and feels fresh. While I prefer olive greens, this one looks decent to me. It feels quite wet, even in drier pens and the flow is good. I haven't experienced any clogging or skipping issues and that's always a plus. Some feathering and bleedthrough will be experienced on absorbent and thin papers.
Overall impression - acceptable. Probably, I'll even use all carts that I bought.
Drops of ink on kitchen towel
My company's notebook (low quality paper), Waterman Phileas, medium nib
Field Notes, Waterman Phileas, medium nib
Rhodia, Waterman Phileas, medium nib
Tsubame, Waterman Phileas, medium nib