multiverse . Is this Vincent’s yellow?

Great visual artists focus on the act of looking. By understanding how humans view art, they were — and are — able to modulate our senses to create an experience, evoke emotion and catharsis. The masters who painted the walls of Ajanta and the Vatican or Impressionists were all trying to tap into our perception.

Artists seek to move audiences with mere lines and colours. It is important for them to develop a keen understanding of how these affect human thought. They have done so through centuries using their observations, experiences of their teachers and, most important, a mix of experimentation and imagination.

Immense effort goes into the fine tuning of an image down to the tiniest differences of colour. So when you view a masterpiece, you might want to make sure that what you are looking at is what the artists saw when they had finished the painting — for that is what they wished to show you.

Time though has not spared the great works of the past. Colours have ebbed without any human intervention. Humidity, oxygen and sunlight are enough to set off chemical reactions that drastically alter the hues of a painting. Yellow becomes brown and orange can turn into white. Since the psychological impact of each colour is very different, we are left with images the artists themselves would have disapproved of.

A painter who used bright colours to produce vivid imagery was Vincent van Gogh. The Dutchman worked for a brief decade, from 1881-1890, producing a style of rich and evocative colour brushwork that would have a lasting influence on modern art. It is from his writings to his brother Theo — possibly his only ardent supporter during his lifetime — that we know of his ideas about painting. Deeply aware that colours would fade with time, he layered susceptible colours thicker in the hope that they might last longer. Alas, his paintings have faded to muted versions. Would it not be wonderful to see them in a form van Gogh would have liked us to?

Over 150 years since his death, the world has changed immeasurably, and so has photography. Beginning with old wooden cameras that projected an upside down image onto a ground glass, we now have handheld phones that can shoot images, apply a host of ‘filters’ to make them amazing and transmit them across continents in an instant.

Consider the immense popularity of the much maligned selfie. It is merely another expression of portrait painting. In the past, it was restricted to those with the financial means to commission a portrait. Commissions were the primary sources of livelihood for artists, but the arrival of machines affected the practice. It is ironic then that the technology that challenged the livelihoods of artists and transformed art is now helping us delve deep into the works of masters.

But it wrestles with some fundamental problems. How can you figure out the intensity of the original colours from a faded painting? A keen eye can differentiate and remember multiple shades, but it is not a practical skill to ask of all humans. So what we need is a way to measure colours and put precise numbers on them. It may be the antithesis of what an artist wants, but bear with me. Pretty much all the colours that we humans see are made by mixing the hues of the rainbow, or, for that matter, three colours — red, green and blue. When we shine white light — a mixture of all the rainbow colours — on an object, it will absorb some and reflect back the rest. The reflected light is what we perceive as the colour of the object.

Both the wavelength of the light reflected (that is, the colour) as well as the intensity (amount of that wavelength reflected) can be measured precisely.

If you are given a large painting that has one colour — for instance, a vibrant yellow that has faded to a muddy brown — your task is twofold. The first is to determine every point on the image that has had the yellow chemical applied. Then you must put a number to measure precisely how much yellow was originally applied. Say, your wavelength measuring machine (called a spectrophotometer) tells you that the wavelength of light being given off by Vincent’s yellow number 1 is exactly 530 nanometre.

The second task is to look at the artists’ notes and reformulate the paint with exactly the same chemicals that they used. You then measure the wavelength of the fresh paint and apply it in varying amounts — from a tiny bit to a lot of it — and then correlate the amount of fresh paint applied to the intensity of yellow light being reflected at that point. When scientists do such measurements they often find that the freshly-made paint reflects a different wavelength of light, say 556 nanometre, which is a more vibrant yellow. In addition, we may find that given the exact same lighting, a spot on the old van Gogh painting reflects 1.54 units of light whereas the new one reflects 1.67 units of light. This spot must now be corrected digitally.

Imagine that you have taken a high-resolution digital picture of an old painting and made a digital copy of the file. Your task is to go pixel by pixel in the original image, look up how much of the yellow chemical was applied at that point and then replace the colour of that pixel (faded) by the colour that you have determined a freshly-made spot of paint should have. At the end of this process, you would have digitally reconstructed the colour of the old masterpiece.

Many such reconstructions are being done today. The soul of many sombre contemplative masterpieces, it appears, is in fact joyous and exuberant, rendered in brilliant colour.

(Multiverse is a new monthly column on manifestations that meld science with art.)

SANTANU CHAKRABORTY

Santanu Chakraborty i s a Bengaluru-based engineer, scientist and photographer