Figure 1.

(a,b) Two examples of commercial products using index-matching fluid (water) to enhance the transparency of a microstructured material to show colour underneath. In the case of (a), a Buddha Board allows temporary art from the dark backing being visible when wet. In (b), a colourful picture is revealed after the board is wet with water. (c) shows a microstructured PE sheet with 13 µm thick pillars attenuating IR transmission. (d) shows an example of the same microstructured PE sheet becoming thermally transparent when wetted with mineral oil.