Lovely ink markers
The Faber-Castell Pitt Artist brush pens have the ink quality you'd expect from the brand, as well as a flexible nib that is delightful to draw and write with.
Additional layers will darken the colour, and once dry it's a waterproof ink. It won't bleed through the paper either, provided you let layers dry (about 20 seconds)
The quick drying time means you have to work quickly if you want to blend or smudge, but if that's what you're after then an alcohol marker might be a better choice.
Great for combining with pencils, or lettering over watercolour etc.
Barrel is somewhere between one and two layers of ink.