Iron gall fountain pen ink from KWZ, handmade in Poland.
PLEASE NOTE: leaving Iron Gall ink in an unused pen for a very long period of time could cause corrosion to occur in pens with stainless steel nibs.
Iron Gall inks should be stored in a cool and dark place to protect them from the negative effects of light on their stability.
Iron Gall inks should not be diluted with water from the tap - the water is rich in various salts and contains trace amounts of the compounds used for the decontamination of water (such as ozone, chlorine, etc.), those compounds will have negative effect on stability of ink. If you want to dilute Iron Gall ink, distilled, demineralized water or boiled water should be used.