Tea is normally adulterated using re-colored used tea, waste (leftover leaves after straining the tea) is collected from tea stalls, dried in the sun, mixed with colours (water soluble coal tar dyes) and some amount of genuine tea to give it the flavour and this mixture is sold as loose tea
There is a simple test to detect if the tea has been adulterated. Take a blotting paper, wet it by sprinkling some water over it and then sprinkle the tea powder over it. If you come across yellow, orange or red spots on the blotting paper, then the tea has been adulterated by using artificial color. Pure tea leaves release color only when they are put into boiling water. Or simply add a teaspoon of tea dust to a glass of water. If you see any patches of colours(as shown in the image) then the tea is adulterated.
PS : We found this method on the internet, if you have any other methods please share it with us as a comment or a mail to firstname.lastname@example.org Not just for Tea, for any food we eat.