Shimmering inks have become very popular in the last year and it’s largely thanks to Stormy Grey. Stormy Grey is part of J. Herbin’s “1670” line of fountain pen inks. 1670 inks are highly saturated and the original formulation of Rouge Hematite (the first ink in the line) was infamous for clogging pens. All four inks in the 1670 line now come with this warning label:
I only use these inks in my cheaper pens and ones that are easy to disassemble and clean.
Stormy Grey contains flecks of gold that tend to settle at the bottom of the bottle and in order to draw them up the bottle must be shaken, otherwise you are left with a much more plain dark grey ink.
Stormy Grey is a very wet ink (perhaps to compensate for the gold flecks?) and this translates to bleeding and feathering on more absorbent papers. The ink worked well on Rhodia but for more porous papers, a thin nib or dry pen is going to be a better match.
I have been using this ink for several weeks now and it performed trouble free in a number of pens until I put some in my TWSBI 580 with a 1.5mm stub nib. In the TWSBI I got spotty performance; sometimes it would write just fine and other times it would choke and skip.
Apart from some gold flecks left behind, Stormy Grey cleaned out of the pens I tested nicely; this was a nice surprise for a highly saturated ink.
Objectively, Stormy Grey is not a good ink but it is attractive and interesting. I can only recommend this ink as a curiosity; it is not a serious every day ink and but putting this stuff in your pen you are risking a clog.