Identifying the chemical makeup of pigment (色素) used in ancient documents, paintings, and watercolors is critical to restoring and conserving the precious artworks. However, despite numerous efforts, scientists had been unable to determine the source of folium, a popular blue dye used to color manuscripts (手稿) in Europe during the middle ages — from the 5th to the 15th century. Now, a team of researchers from Portugal has finally uncovered the mysterious ingredient responsible for the gorgeous blueish-purple color that helped bring ancient illustrations and texts to life.
The research team began by poring over instructions penned by European dye makers from the 12th, 14th, and 15A centuries. They found what they were seeking in a 15th-century text entitled The Book on How to Make All the Color Paints for Illuminating Books. However, translating the instructions was no easy task. It was written in the now extinct Judaeo-Porluguese language, and though the source of the dye was traced back to a plant, no name was mentioned.
However, by piecing together suggestions from the text the scientists were able to determine that the dye was made from the bluish-green berries of the chrozophora tinctoria plant. After an extensive search, the team found a few varieties of the plant growing along the roadside near the town of Monsaraz in south Portugal.
The detailed instructions gave the researchers critical clues — including the best time to pick the berries. "You need to squeeze the fruits, being careful not to break the seeds, and then to put them on linen. The scientist says the detail was important since broken seeds polluted the pigment producing an inferior quality ink. The dyed linen, which was left to dry, was an efficient way to store and transport the pigment during ancient times. When needed, the artist would simply cut off a piece of the cloth and dip it with water to squeeze out the blue color.
Once the key ingredient had been identified, the researchers began to determine the dye's molecular structure. To their surprise, they found that folium was not like any other known permanent blue dyes — it was an entirely new class of color, one they named chrozophoridin. "Chrozophoridin was used in ancient times to make a beautiful blue dye for painting. " the team wrote in the study. "Thus, we believe that this will not be our final word on this amazing plant and its story and that further discoveries will follow soon."
