Some of the most brilliant colors found on butterflies, birds and squid are produced by nanostructures on wings, feathers and skin that reflect light. The effects can become even more varied when these “structural” colors are combined with filters made from light-absorbing pigments. For example, the characteristic green plumage of parrots seems to be produced by yellow pigment over a blue reflective nanosurface. The purple wing tips of Purple Tip butterflies come from red pigments beneath a blue iridescent nanosurface.
A better understanding of how these effects are achieved could give painters and visual artists entirely new ways of making colors based on iridescent and pearlescent pigments, which so far have been largely restricted to less sophisticated applications in the automobile and cosmetic industries.
Painter Franziska Schenk has been exploring the mixing of structural and pigmented color during her stay as artist-in-residence at the University of Birmingham’s department of biosciences in the U.K. With iridescent particles, Schenk says, “the established methods of easel painting no longer apply. Their conversion to painting requires something truly innovative.”
Schenk used iridescent particles to reproduce the starting blue of the Morpho butterfly wing in a series of paintings that change color when lit or viewed from different angles. The background color on which the particles are placed is central to the effect. On white, the light not reflected from the blue particles passes through and bounces off the base; when not seen face-on, the blue quickly fades and is replaced by a muted yellow. But on a black background, all non-blue light is absorbed and the blue is more pure and intense. “It’s impossible to represent my work in still images,” she cautions, but we will try here (see below). “To fully appreciate the effect one has to move around the work and view it from different angles.”
Morpho butterfly wing, painting by Franziska Schenk, lit from different angles.
The brilliant colors take advantage of recent improvements in synthetic pearlescent particles. The earliest of these were made by coating mica flakes with multilayers of metal oxides. But because the mica surfaces were not perfectly smooth and the grain sizes varied, the precise colors and intensities of the particles varied. Schenk has used pigments in which the mica substrate is replaced by a transparent borosilicate glass, which is smoother and gives a purer hue.
Schenk believes that “iridescent technology is destined to introduce a previously unimaginable level of intensity and depth, thus adding beauty, luster and a dynamic dimension to art.” Her Studies of Cuttlefish (below) uses iridescent flakes mixed with beads and wax.
Studies of Cuttlefish by Franziska Schenk, using iridescent flakes mixed with beads and wax.
Another series of cuttlefish, Mantle of Many Colours, was done with iridescent paint that differs in appearance depending on the conditions and angle of lighting, which results in a compelling chameleon effect that traditional paints simply cannot create (below). The colors change from greens to purples as the viewing angle shifts.
Mantle of Many Colours by Franziska Schenk, which uses iridescent paint, as seen from different angles.