Complex sentence: In 1834--1835 potassium ferricyanide was used to bring out faded or eradicated ink, which had the effect of defacing the vellum from green and blue to black and brown.
Split into simpler sentences: In 1834--1835 potassium ferricyanide was used to bring out faded or eradicated ink. The vellum defaced from green and blue to black and brown.