Rohrer & Klinger´s writing inks are produced in the old traditional way with high quality colourants, specially treated water and minimal amounts of additives. This colour-intensive ink is suitable for use with fountain pens, quills (Isograph pens), cartridge converters and other calligraphy utensils. Among the 18 different ink colours are two iron gall inks that will become archival safe after being allowed to oxidize in the air (i.e., dry). The Permanent Blue ink is also very hardwearing and, in contrast with Royal Blue, cannot be removed by means of a liquid solvent. All the inks can be mixed with one another. A mixture that includes the Sepia coloured ink must be immediately used and the fountain pen quickly cleaned thereafter.