High-quality oak-gall-ink with best writing characteristics! Manufactured in Switzerland. The dark blue colour changes after a few days into deep black, then waterproof. Real oak-gall-ink reacts on the oxygene in the air and gives the user the opportunity to control this reaction individually: the longer you leave the bottle opened, the darker and viscous the ink gets. Not for fountain pens! In a 30ml nostalgic flacon with cork, sealed.