The freshly tapped sap of the rubber tree is also known as ‘Latex milk’ and, like cows’ milk, it has to be treated to prevent it from going bad.For this purpose, latex traded in liquid form is centrifuged and then ammonia is added. The resulting product is Cenex which is the basis for all dipped products such as ball bladders, balloons, condoms and household gloves.

For solid rubber, the latex milk is coagulated by adding acis (similar to yoghurt). Any water is then squeezed out and the resulting raw material is dried either in the open air or over a fire, in some cases with added smoke. These semi-processed stages are known as Pale Light Crepe (PLC) and Ribbed Smoked Sheet (RSS), with both traded in varying quality ranges. For example, the dark sole of a sneaker will be made from RSS, the white parts from PLC, and then Cenex is used as the glue to hold it all together.

There are hundreds of plants which produce rubbery juices. However, over the last century, the only one with commercial relevance is the sap of the tree Hevea Brasiliensis which grows in the Amazon rain forest. This is the true ‘rubber tree’ and is not to be confused with the ornamental Ficus Elastica. For centuries the indigenous inhabitants of the Amazon region were aware of the elastic and waterproof traits of the sap from the rubber tree.

However commercial relevance only came with the vulcanization process invented in 1840 which turned rubber into a durable material so that it lost its stickiness and no longer melted in the heat. In 1876 Great Britain succeeded on a questionable legal basis to ‘secure’ 70,000 rubber tree seeds from the Amazon; this became the basis for the rubber plantations in South and Southeast Asia which today dominate the natural rubber production. The four biggest producer countries are Thailand, Indonesia, Malaysia and India.

For the first time, in 1913/14, rubber sourced from plantations overtook the volume of rubber that had been wild-tapped in the jungle. The main user of rubber was, from the very beginning, the automotive industry; in 1900 there were one million cars globally and around seven million bicycles, all doing their bit to increase demand. The world wars increased demand while at the same time supply chains were compromised. This led to increasing research efforts to come up with artificial rubber. By the end of the 1950s the production of synthetic rubber overtook that of natural rubber meaning that today approximately 60% of the material referred to as ‘rubber’ is synthetically produced from petroleum. This has replaced natural rubber not only because of the cost but also due to specific quality parameters. However, for certain premium products, like top hot water bottles or the tyres of jumbo jets, there is no substitute for natural rubber.

But none of the large-scale production of natural rubber would have been possible had it not been for the appalling cruelty that accompanied it. Brute force was used to force the indigenous populations of the Congo and the Amazon to tap rubber. If they failed to meet arbitrarily set tapping ‘targets’ they had limbs cut off and if they tried to resist, they were slaughtered. One estimate claims that in the sourcing of the rubber for the tyres on one Model T, four people would lose their lives in this way. In the Amazon, at least 30,000 people were killed in the race to source rubber.