Different Color In The Last Bit Of Ink Sitting At The Bottom Of A Bottle?

[Cursive Child]

I've had this bottle of Iroshizuku Ku-Jaku for about 8-9 years. Finally getting to the bottom of the bottle. Noticing that the color is quite different on paper than it was a few fills ago. It's bluer and darker, even in the same pen. I know the original color used to dry to a greenish blue - Pelikan M605 Medium nib on Staples sugarcane paper.

 

Why? Is it because the ink at the bottom wasn't shaken or stirred, and somehow, the bluer color was heavier? I didn't notice anything, but frankly never looked and it's a dark ink anyway.

 

I've forgotten my high school chemistry, but if it's a dye based ink, why would it do that?

 

I don't use much ink, so each bottle lasts for years.

 

Anyone else have this happen to them with a bottle?

Edited November 1, 2019 by rdugar

[DonM]

Short answer is evaporation. Happens with plastic cartridges, too. Makes the ink more dense.