The plasma of an atmospheric pressure plasma jet strongly interferes with a liquid when it just touches the liquid surface. The gas flow of the jet exerts a force on the liquid surface pushing it downwards, while the plasma exerts a force which is partly counteracting the gas flow induced force. The downward force in the centre of the liquid recipient causes the liquid to circulate with a circulation time of ~2 sec. Due to this circulation the color change of a dye proceeds homogeneously.
Rens, van, J. F. M., Schoof, J. T., Ummelen, F. C., van Vugt, D. C., Bruggeman, P., & Veldhuizen, van, E. M. (2014). Induced liquid phase flow by RF Ar cold atmospheric pressure plasma jet. IEEE Transactions on Plasma Science, 42(10), 2622-2623. https://doi.org/10.1109/TPS.2014.2328793