The Grand Pepper Shaker Mystery

So we have this pepper shaker made of glass with a print on it.

One fine dinner, it ran out of pepper, so I opened the lid to fill it in and noticed a peculiar thing – small particles of pepper dust were stuck to the inside glass walls but only in places, where the print wasn’t present on the other side. Everywhere directly behing the print, the pepper particles almost didn’t stick to the glass.

(These photos also show vertical traces from a spoon, which are not relevant, I hope you’ll see the phenomenon anyway.)

I’ve been wondering about this for a while and been thinking whether it’s got to do with light, or light and humidity, or electric charge… But as for now, I don’t have the final answer, so I’ve decided to ask the Internet.