Recently, I got myself a bottle of Monteverde Fire Opal - because I liked the colour, but also because I hoped that it might finally prove to be that rare ink in this particular colour range to be free of nib crud issues.
Alas, I have now found that it suffers from the same sort of nib crud that users of similar-coloured inks like Diamine Ancient Copper will be familiar with. When used in pens with a less-than-perfect cap seal, the usual frothy crud builds up. The same happens during long writing sessions - crud gradually builds up along the length of the nib slit and the nib-section and nib-feed interfaces, and needs to be wiped off every now and then.
After having owned and used three inks from different manufacturers in this colour range - Diamine Ancient Copper, Private Reserve Orange Crush, and now Monteverde Fire Opal - and having experienced nib crud issues with all of them, I have now resigned myself to the understanding that, so long as I am using a rusty/coppery-coloured ink of this particular type, there shall be no escaping nib crud.
It's just a cosmetic and convenience issue, but still rather annoying.