A seventeenth-century army increasingly relied on gunpowder, and the production of that vital resource required three mineral ingredients - charcoal, sulphur and saltpetre. Of these, the two minority ingredients were charcoal, which could be obtained readily wherever there were trees, and sulphur, which was mined in many places and was fairly cheap. However, three-quarters or so of the mix was taken up by saltpetre, the mineral potassium nitrate. Saltpetre forms naturally in small quantities in some locations, but for regular supply it had to be 'farmed' by heaping animal dung with earth in large beds that were then treated with urine for a period of months. Bacterial action produces potassium nitrate, which with the right technique can be refined to a relatively pure crystalline product.

The Mughal army was as gunpowder-based as the European armies. At the start of the sixteenth century the technologies were very similar, with European powers making advances in the seventeenth. However, to the end of the seventeenth century, Mughal central power was still strong, and the empire reached the high point of its territorial extent under Aurangzeb (r. 1658 - 1707). Gunpowder production was well organised, and Bengal became one of a few regions where saltpetre production was concentrated. The English and Dutch with their presence on the Hooghly River could also purchase quantities here for export to Europe. The main production centre was a short way upstream:

The saltpetre produced at Patna was considered the best in quality for making gunpowder. .. The European Companies generally exported refined saltpetre as otherwise it could not be used for making gunpowder. Moreover, the export of raw or crude variety was uneconomic as it increased the freight charges while customs duties remained the same on both refined and crude varieties. The Companies often undertook the refining in their own factories.(Chaudhuri p. 162)

The English Company regularly sent requirements for saltpetre to be delivered to London, or to Madras to build up stocks at Fort St. George. Typically they asked for anything between 300 to 1,000 tons annually (p 164-5). The Dutch probably produced even more, as much as 1,500 tons.

Between 1650 and 1720 the price of saltpetre in Bengal roughly tripled due to the constant heavy demand from the European companies as well as local rulers including the longtime governor of Bengal, Shaista Khan, and one of his successors, Azim-us-Shan. They used the usual combination of force and bluster to extort concessions form the Europeans.

The only inhibiting factor [in the way of saltpetre production] was the occasional attempts, though never pursued vigorously or systematically, by local officials to monopolize the trade. Mir Jumla made such an attempt but with little success. The next subadar, Shaista Khan, tried to monopolize the trade and sent his agents to Patna who 'obstructed and hindered' the procurement of saltpetre by the Europeans. When the English appealed to him, he demanded 20,000 maunds [approximately 670 tonnes, taking the maund at 74 lbs] of saltpetre from them on the pretext of his Arakan war. Prince Azim-us-Shan also made a similar attempt in 1699. He sent an agent to Patna to buy between 40,000 and 50,000 maunds of saltpetre on the plea of making gunpowder for his intended attack on Arakan.

Sources

Chaudhuri, Susil. Trade and commercial organization in Bengal 1650 - 1720 (Calcutta 1975)

The Medieval Gunpowder Research Group at Leeds University have done extensive research on how the constituents of powder were produced. They have recreated the saltpetre heap