I have an old, pre-reformulation glass bottle of Diamine Blue-Black, and a pre-reformulation glass bottle of Diamine Onyx Black.
Both of these inks were purchased around 2010 and have been used periodically since then, but not very often as I don't particularly like the purple undertone of the black, and the teal undertone of the blue-black.
Recently, I have noticed that both inks are drying out in multiple different pens' feeds after they have been unused for a day or so. If the pen is shaken then some ink enters the feed and a dozen or so words can be squeezed out before the pen runs totally dry again. Even then, ink flow is much reduced and proper flow can only be restored by priming the feed.
For many years these inks flowed perfectly. I wonder if perhaps the inks have thickened, so to speak, as air has evaporated. Or perhaps they have just chemically degraded. I have noticed that the blue black appears to have some small solids that are adhering to the inside of the glass, even through the ink itself looks perfectly liquid otherwise. Both have been stored in a dark and relatively humid closet with a stable environment.
Does anyone else have experience of inks degrading over time like these Diamines? Is this, perhaps in part, why they were reformulated?