Fig. 6 Vertically (top) and horizontally averaged (bottom) relative Brilliant Blue and Azophloxine concentration distributions of the profiles at 5, 7.5, and 10 cm distance from the wall in the dry sand (DS) and wet sand (WS) columns obtained from the concentration maps (Fig. 5 for Brilliant Blue). Vertical concentration distributions obtained from horizontal sections taken at 0 to 5 cm from the wall are also shown