 When goldbeater's skin or ox skin is dipped in HCl, rinsed in water, soaked in the tannin solution for 5 minutes, washed in water, and then treated with 1% FeSO4 solution, it gives a blue black color if tannin was present.Use of ferric chloride (FeCl3) tests for phenolics in general.Powdered plant leaves of the test plant (1.0 g) are weighed into a beaker and 10 ml of distilled water are added.