Laughing myself sillier.
I stored my inks for more than a decade in a NON temperature controlled caboose.
+1. This is the right answer. It is the only right answer above. Literally we do not know how long we may expect inks currently made under EU regulations to last. We can't know. The time has not passed that would enable us to know. Not all questions have immediate answers.
We have an idea that inks made in the 1950s may be used today. That is because the 1950s have already happened and the decades have passed. Inks made today in Europe are not the same as the inks made in long-past decades and the time has not yet passed that would enable us to predict the longevity of those inks. With Japanese inks made today, go for it.
However, I have tested inks in the bottle by putting them into a sunny window that gets afternoon sun in Las Vegas.
The detailed report is here in a thread, but you can see the photos here: http://www.sheismyla...ndow/index.html
another caveat -- don't store your ink in the general vicinity of your houseplants, as potting soil is teeming with assorted symbiotic microbes, many of which are happy to infect your ink.
Iron gall inks will degrade as they are exposed to oxygen, but you generally only find such inks when you go looking for them.
The vintage IG inks I had (as in Pelikan Blue Black and Carter's ink) were some of the only ones to degrade.
AND when we were doing testing for powdered inks, we found that houseplants were a HUGE problem for inks.
I am far more interested to know what the O.P. (or anyone else) deems observable ‘signs of degradation’, and whether the premise is that the ink is put into storage unopened for five years, or being used to refill pens from time to time over that period.
I think degradation is where the color changes from orange to green (some of the older PR inks did this) or it develops STIB or it becomes unusable.