Based on archival material in the Lower Saxon State Archives, in 1792 the Prussian government purchased from the apothecary of Johan S. F. Mertens of Neustadt-Eberswabe, the secret of a blue dye. This dye was for dyeing paper in the Dutch way and was used in several paper mills. The recipe or process to manufacture this color and the nature of it was lost and remained unknown until some 50 years ago, when hand-written records in the Unterfichten Mill near Schwabach (Bavaria) revealed that the knowledge of the above really was available throughout the years. The process to produce writing paper is considered very delicate and elegant, although cumbersome. It took a large quantity of horn shavings as well as a smaller specified quantity of thoroughly purified salt of tartar. It also took large quantities of water, both cold and boiled, iron- vitriol, and pure iron (using nails). Also needed were utriol-oil, vitriol-acid and alum. Earthen pots, not glazed, but lined with clay bricks and leaves of ferric oxide, as well as large iron kettles were need. Coal dust was used for covering and linen cloth with double printing paper for straining and filtering. It took several steps from cooling to boiling, from smelting to baking. Above all, it required very precise measurements and timing of the many individual steps of the process which was tremendously long and time consuming.