60ml: Dye ink
Blue black ink (water-based dye ink)
Blue black ink is not affected due to sunlight or humidity, and it has high water resistance, which makes it ideal for permanent records.
Initially, it had a unique feature and was initially released as an ink for long-term storage for official documents, but has been discontinued by major manufacturers.
The origin of this ink dates back to the 2nd century, and its widespread use was in the 12th century. Initially, it was made from nuts and sap, and in the 16th and 17th centuries it was used in wine and beer as a fungicide.
The current ink was established in the 19th century.
The manufacturing method uses an oxidizing effect that ferrous ions turn into ferric ions to form the color black. Thus, it is not an ink that mixes blue and black inks, and a dye or acid is added.
Hence, the blue black ink is not "bluish black" or "blackish blue", but it is blue at the beginning of writing, but the blue color of the dye over time changes into black due to its scientific function to maintain long-term records. Only the black part of the iron that has been mixed remains on the paper's surface and becomes black because it has become dim.
Simply put, it turns blue at first and then turns black over the years.
It can be said that the deep dark blue color is obtained with this ink.