vintage ink Vintage Parker Blue Black Ink

[kcwookie]

I've purchased several bottles of vintage Parker Quink Blue Black. Some are in the 1940s bottles and some the 50s. Most are a shade of black gray and somewhat watery. The color is very pale. I have a few bottles that the ink is more blueish, but still blue black. Does anyone know the chemistry behind this?

 

On a different front, with some of the vintage ink I've used, adding a few drops of water make the ink more dry and improve the color. It seems counterintuitive.