Electronic circuit boards use thin layers of copper sandwiched between layers of epoxy resin to connect components.
Combining copper with nitric acid produces nitrogen dioxide, a poisonous brown gas with a sharp, biting odour.
This was quite a difficult shoot. For fairly obvious health and environmental reasons, Sanjay's work is illegal in India. The police and authorities turn a blind eye to the activity in return for bribes, and the compounds where Sanjay and his friends work with the acid (Sanjay called it his 'hole') are rented from some fairly unpleasant gangster types who weren't keen on having someone with a camera hanging around.
It took a long time to get access to the area and for the workers to begin to trust us enough to talk about their work and allow us to film them. Just as Sanjay and his friends began to trust us, the landlords started threatening them with violence and eviction if they continued to have any involvement with us. We had no choice but to leave to avoid causing trouble for them.
So I have mixed feelings about this film, knowing that we had to stop filming right when I felt we were just beginning to make something quite special with Sanjay. The workers in each compound usually all come from the same village, most having migrated from rural Bihar State, India's poorest province. I was struck by the similarities between their new work with the copper and the agricultural labour they had left behind. The unhappy irony being that their work now poisons the same land which used to grow their crops.