By the end of the 19th century the textile industry was experiencing tremendous growth which fostered a need to develop faster and more economical rug dyeing processes to keep up with the demand for increased production. Until this time rugs were dyed using natural materials such as root madder and insect shells.
Aniline was the first synthetic dye dated around 1826 developed by a German chemist Otto Unverdorben. Many early developed synthetics used in rug dyeing were not successful and caused a multitude of problems such as bleeding when exposed to water, fading and color change. Over time synthetic dyes improved. Using technology to create synthetic dyes offered the ability to create hundreds of different shades of color that even experts find challenging to distinguish from natural dyes. Today to verify the authenticity of antique rugs from a dye perspective, liquid chromatography and photoelectron spectroscopy can be utilized to make the distinction.
Identifying the presence of synthetic dyes in rugs can be used to help determine age. Antique and semi-antique rugs are dyed primarily with natural materials; however there are older rugs that may have the presence of a few synthetic dyes. The dyes used in the rug making process are crucial in classifying a rug as collectible woven art or primary purpose is decorative.
I learned a great deal about dyes from noted authority Manfred Bieber. John Collins has also enlightened me as to the importance of natural dyes to qualify a rug as woven art.