I make all my inks in my North Wales Studio from natural dyes. Black is made from a oak galls and it was the way black ink was made for centuries, in the West that is the Chinese used soot black. The black is made form a combination of the tannin in the oak galls and iron ( Ferrous sulphate) Painted into paper it is nearly colourless and slowly ( over 5 minutes or so) oxidses into black in the air. The 18th century in the title refers to the fact that logwood is added to the mixture folowing an 18th century recipe so when the ink is first painted on it it looks a dark grey .
All my inks were exposed to sunlight in a south west facing window for one month. The black did not fade so has a lightfastness of 1, it is however corrosive over a long peroid of time. High quality watercolour paper may degrade in a 100 years or so.