MULTIVERSE . Blue is the warmest colour

I’m walking along a village path just after a rainstorm and look up at the morning sky. It’s lush blue, pristine and clear, and has puffy white clouds billowing out of nowhere. It is the kind of sight that has had the painters hooked. Yet, when inspiration struck the ancient people, they often found themselves short of one colour: Blue

Humankind has been painting for ages. Painters who worked the walls of ancient caves and rock shelters, such as those in Bhimbetka, Lascaux and Altamira, had access to numerous colours. They simply ground the earth, mixed it with glue and applied it on the walls. Soon they started extracting dyes from plants. But plants offer a limited range of colours — mostly green and brown, also red, orange and yellow. Of blue we see very little. It turns out that nature does not make enough blue, certainly not in large quantities. So what is an aspiring painter to do?

With our present-day distractions, we may not observe nature as much as the ancient people did. But clues to producing pigments are scattered all around us. Leaves on a tree are mostly green, or a shade thereof, but they also change colours when they dry and fall off. Some leaves turn bright orange and yellow, some are red when they wilt. In some parts of the world, entire forests turn a riot of colour. In others, such as the Indian plains, the displays are less dramatic — say, the bright yellow of a dying papaya leaf in the backyard — but they are nonetheless very instructive. Is it possible then that air, water, sunlight and the multitude of microbes around us can play a part and entirely change a leaf’s colour? And will a few leaves, initially a shade of green, turn blue after an artificial treatment?

This, it turns out, is a real possibility. A few species of trees produce leaves which, after soaking in water, release a green liquid. This liquid when fermented turns bluish. This sediment-laden water is boiled at a high temperature for a few hours. The new sediment when filtered reveals a deep, rich, blue substance, which is then dried into cakes. This is the process of making the dye called indigo. It is definitely a complex process, but one that humans were motivated to work out thousands of years ago. The earliest examples of using indigoid dyes come from the Peruvian archaeological site of Huaca Prieta almost 6,000 years ago. The Egyptians were familiar with indigo about 4,400 years ago and it was used in Xinjiang 3,000 years ago. Today indigo is possibly the most popular blue around. Just look at jeans.

The discoveries from archaeological sites around the world suggest that humans have long been intensely attracted to blue. It was only a matter of time before the search for other shades of blue became a serious affair. The Egyptians worked out a method to manufacture synthetic blue as early as 5,000 years ago. They did so by heating sand, lime, copper and some ash to about 1,000 degrees Celsius and were rewarded with a crystalline ‘Egyptian blue’. It was possibly the most popular blue in ancient times and its regular use has been documented till the Roman era. They also used other naturally occurring copper minerals such as azurite, which is used in colour pigments to this day. The Spanish master Diego Velázquez’s painting The Surrender of Breda (1635) features this soft, mellow azurite blue.

But the quest for a more dazzling blue continued. A brilliant blue that met the seekers’ standards was found in a mine in the Badakhshan province of Afghanistan. So prized was this blue that it was used on the young Egyptian pharaoh Tutankhamun’s funeral mask and, closer home, in Ajanta caves as well as the Indus Valley ornaments. The raw ore of lapis is a deep blue, but with scattered impurities. Could you grind the stone and extract just the pigment? Only the intense blue particles and nothing else? Artist-scientists set to work. Their fundamental idea was elaborated upon by the Renaissance artist Cennino d’Andrea Cennini in a manual, Il libro dell’arte . The quest for this intense blue may have been driven by the artists, but the method employed to get there was purely scientific. The lapis lazuli is mashed into a powder and kneaded into a dough together with plant resins and wax that are empirically found to bind everything but the blue pigment. When you wash this blue dough in water, what emerges is the precious pure pigment of Badakhshan. Lapis lazuli is thus transformed into pure dazzling ultramarine. It is the colour with which Vermeer continues to dazzle us to this day.

Further explorations into blue pigments happened in the middle of the 16th century. A combination of scientific and industrial methods produced a wide palette of blues, many of them synthetic versions of precious pigments of the past. Some like phthalocyanine blue not only became the pigment of choice for mass production, but also endeared itself to modern masters such as Piet Mondrian and Jackson Pollock.

New versions of blue continue to be made by scientists and coveted by artists. Next time your eyes catch a shade of blue, it may be the time to remember humankind’s long and inexplicable affinity to the elusive colour, one that draws us a tiny bit closer to the infinite sky and the vast oceans.

SANTANU CHAKRABORTY

Santanu Chakraborty is a Bengaluru-based engineer, scientist and photographer

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