Twenty-five hundred years ago, Democritus of Abdera said "there appears to be heat, there appears to be cold, there appears to be color. In reality, all there is are atoms and the void."
Amazingly enough, this is pretty much the picture modern science has of the world. There are only atoms surrounded by space or the void. The concepts of heat and cold are feelings we have.
And as Jean Dubuffet put it in 1973, "there is no such thing as colour, only coloured materials."
Atoms and molecules are not coloured objects.
The colour around us is a matter of perception. It is a consequence of the way light receptors in our visual system respond to the world. Things are only coloured because we perceive them to be. Beauty may be in the eye of the beholder, but so is colour, shape, form, pretty much every aspect of everything we see.
Artists play with this perception.
And over the past few weeks, I've been talking about oil paints as a way of discussing the science in art and the art of science. We have been discussing pigments and dyes along with the compounds used to makes some of them.
All of our paintings are two-dimensional representations of a three-dimensional world. They trick our senses into seeing light and shadow, background and foreground... into seeing the world through the eyes of the artist.
But at the very heart of it all, inside the chemical compounds, there is no colour.
The technical explanation for what we see is derived from quantum mechanics. Photons of light interact with matter through electronic transitions. Ground state electrons can absorb the energy of a photon elevating the electron to an excited state. Alternatively, excited state electrons can emit a photon dropping the electron to a ground state (or some lower energy excited state).
Absorption and emission define the subtractive and additive nature of colour in paintings and light. Pigments and dye absorb some wavelengths while reflecting others. For example, a blue pigment appears blue because the molecules and atoms within the compound absorb yellow light. The blue we see is the light left over after the absorption. Painting with all of the pigments blended together results in the absorption of all the light and ultimately yields a black colour.
In contrast, light is generated by emission and coloured light, such as used in theatre lighting, adds up to white light or the whole spectrum. The blue, in this case, is the portion of the visible spectrum corresponding to the blue light with the other colours blocked out. Sunlight contains all of the wavelengths from indigo to red and many wavelengths beyond but it is the rainbow which we see in the sky which represents the visible components of the electromagnetic spectrum.
This is, perhaps, not the way most artists would think of their paintings - a subtle blending of the absorption properties of chemical compounds but it speaks to the essential role of chemistry and physics in art and of how atoms interact with each other.
And why it is so hard to paint light.
There is more to this whole picture.
Over the past weeks, we have made the distinction between pigments and dyes. In general, pigments are considered to be colour-fast or not susceptible to photochemical degradation. They are generally made of metal ions such as cobalt, chromium, or copper. In each case, the metal ion has electrons which can move from one energy level in the ion to another.
But they stay within the atom.
The size of the jump the electron takes is influenced by the atoms surrounding the metal ion. Various shades of blue and green can be obtained from copper complexes, for example. But no bonds are disrupted during the process.
Dyes tend to be organic molecules where colour is obtained by transitions within bonds. That is, within the cloud of electrons holding two atoms together. The colour obtained is influenced by the atoms involved in the bond. But it is also more susceptible to bleaching as these electronic transitions can break up the molecule by destroying the bond.
Of course, while the materials in a painting give rise to absorptions, colour is a matter of perception. We have three different colour receptors or cones in our retina corresponding, roughly, to cyan, magenta, and green along with the rods which discern the gray scale. It is the combination of these receptors in our eyes and the processing in our brains which we perceive as colour. The processing part actually explains why different people can see the same colour in a slightly different way.
There may not be colour.
There may only be atoms and the void.
But the world of art takes advantage of our perceptions and quantum mechanics to give us something more.
