Classic Solution

Sir John Herschel was the first to discover and utilise the brown Ferric Ammonium Citrate (FAC) in conjunction with Potassium Ferricyanide (PF) for creating his prints. The brown hydrated variant comprises approximately 16.5-18.5% iron, around 9% ammonia, and 65% citric acid.

When applying the classic solution, a longer exposure to ultraviolet light is necessary as it holds a higher iron compound content in contrast to the Valenta solution.

Because of its (Classic) higher values in iron, certain papers may exhibit a subtle off-white hue due to the elevated concentration of iron in the classic solution. The extent of this effect varies depending on the construction of the paper.