Sublime Indigo in Timor

We have come up against a surprising bottleneck in our work to expand the production of natural indigo dye paste beyond its traditional scale to create new community businesses in Timor. The restriction is in is the availability of high quality slaked lime, which is used both in the making of indigo paste and the preparation of an indigo vat. Threads of Life's Timorese field staff, Willy and Yansen have been meeting slaked lime producers to learn their methods and coordinate production to fulfill the paste-making needs of the indigo farmers we are working with.

To make indigo paste, leaves of an Indigofera tinctoria are packed tightly in a soaking vat and covered with a minimum of water and left overnight until the indigo precursors leach into the water. After the leaves are removed, slaked lime is added to the soaking water at 2% of the original leaf mass, and the water is aerated by agitation, or pouring or pumping the liquid back into itself. This is done under the alkaline conditions created by the slaked lime so that the precursors react to produce indigo pigment. Indigo pigment particles are too small to precipitate from the soaking water unaided, so the slaked lime also precipitates the pigment. After settling, the water is decanted and discarded so that the paste can be collected. To make a dye vat from this paste, more slaked lime is added to raise the pH to 10-11, and a source of reducing sugar is added (barks, woods, roots, fruit, or even indigo leaves are added) to convert the dye into its soluble form.

Left/Above: picking burned limestone from the remains of the charcoal and cow dung fire. Right/Below: Slaked lime ready for storage.

The slaked lime used in these processes is made by burning limestone, coral, seashells, or snail shells to turn calcium carbonate into calcium oxide (quicklime) and then slaking it with water to produce calcium hydroxide (slaked lime). Unless kept in carefully sealed containers or used soon after production, the drying calcium hydroxide releases its water and reabsorbs carbon dioxide to return to inert calcium carbonate that is of no use to the indigo paste maker or dyer. Quicklime is produced industrially in Java and sold in Java and Bali, but it is dangerous to transport as it reacts very exothermically with water. A few spoons of quicklime added to a few liters of water will cause the water to boil and will even melt through a plastic container. Imagine a shipment getting rained upon en route to Timor!

In Timor, limestone is used for making slaked lime. It is sun dried for 3-4 days, then a fire is made of dried coconut fronds and the limestone is placed upon this. Nearby, a circle of dried cow dung is arranged on the ground and covered with charcoal. The heated limestone is placed on top of this and covered with more charcoal. A further layer of dried cow dung covers this before the pile is set on fire and left to burn for twelve hours. The burned limestone is then placed in a woven palm leaf basket and doused with water. It is wrapped in banana leaves until use.

Sold in small quantities through local markets, consumers keep their slaked lime in sealed containers made from bamboo, wood, cow horn, old plastic bottles, or anything else that keeps the air out. This works well for the amounts used during preparation of the betel nut quid and for small-scale indigo paste making and indigo vat preparation. But for an indigo farmer processing several hundred kilograms of leaf per day during the harvest season, a few kilograms of slaked lime are needed every day, and it is not produced at that scale locally and will have to be ordered to have good quality slaked lime in the right quantities at the right time of year.