High-quality oak-gall-ink with best writing characteristics! Manufactured in Switzerland. The grexish blue colour changes after some time 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 50ml plasic container with wide opening for Ruling Pens and Automatic Pens.