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Standardization of Natural Dyes

Padma Vankar is researcher from the Indian Institute of Technology and she has a long experience in natural colourants and their verification in India. She has been involved in natural dye standardization in India where standards have been created for eleven different dyes.

Standardization of natural dyes is important in substance authenticity and discovering falsifications. Unfortunate are the fault actions that may exist: more expensive natural colourant can be replaced by cheaper, natural colourant may be partly replaced by synthetic one (i.e. mixture), or synthetic dye may be sold as a natural one.

In standardization, the following questions are important:  What is the need of standardization of natural dyes? How does standardization help the producer and the buyer? Can Natural dyes be used and applied in the same way as synthetic dyes in industrial scale?

Repeatability and reproducibility of the particular colour is a very important requirement in industrial dyeing. The dyeing result should be the same regardless of the dyeing batch. Standardization of the natural colorant is required in order to be able to scale up the production of dye and dyeing from laboratory scale to industrial scale. Therefore, the verifying of the dye and its content becomes mandatory and systematic analysis by chromatography and spectroscopy is required.

Chromatographic analysis by thin layer chromatography (TLC), high performance thin layer chromatography (HPTLC) and high pressure liquid chromatography (HPLC) needs to be carried out. These methods reveal the characteristics of a particular natural colourant. Further, analysis by UV-visible spectroscopy is important. Based on calibration of the visible spectrum, the dye content is calculated and subsequently the recipe can be set for different shade depths of the natural dye. The chromatogram and the spectrum for each colourant can be made available in a database so that if an unknown dye powder has to be tested for its natural origin, the developed data base can support to match them. This will help both the producer of the natural colourant and the buyer. Authenticating the natural colourant is very important in also when setting the price for the dye.

Writer: PhD Padma Vankar, Indian Institute of Technology 

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Photos: Riikka Räisänen

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