Saltpeter Production in Gokayama
Traditionally, one of the main industries in the Gokayama region was the production of saltpeter (potassium nitrate) from the mineral niter, an essential ingredient in gunpowder. The saltpeter industry operated for over 300 years during the rule of the Kaga domain in Gokayama, growing exponentially after the introduction of European matchlock guns in 1542. The production of saltpeter in the area was kept secret even from the shogunate (the ruling military leadership of Japan) in order to strengthen the defense of the Kaga domain, which bought up large amounts of saltpeter every year. Gokayama was an ideal location for secret niter production as the area was isolated and much of it remained unexplored.
Saltpeter was created in a hole up to 2 meters deep under the irori fireplaces of the gassho-zukuri (steep thatched roof) houses of the Gokayama region. The hole was filled with a mixture of materials including straw, soil, mugwort, and silkworm excrement, then left to ferment for around five years. The irori fireplaces were used to keep the materials warm during the fermentation process, and the materials in the hole were mixed together once a year to expose them to air and to add in extra ingredients. Over time, calcium nitrate formed in the soil through the nitrification of bacteria. To extract potassium nitrate from the soil mixture, water and soil were mixed together, and the water into which the calcium nitrate had dissolved was concentrated through heating. Grass and wood ash were then added to the concentrate to remove impurities. The potassium carbonate contained in the ash reacts with the calcium nitrate in the concentrate to form potassium nitrate and calcium carbonate. The calcium carbonate precipitates because it is insoluble in water. The liquid is then filtered, boiled down and condensed, and then cooled to obtain coarse saltpeter crystals. The collected saltpeter crystals were sold to the Kaga domain and delivered to their warehouse in Kanazawa. After the abolition of the feudal domains in 1871, the Kaga domain ceased buying saltpeter. During the Meiji era (1868–1912), cheap saltpeter was imported from Chile, resulting in a decline in local production.
Today, visitors to Gokayama can visit the Saltpeter Museum, also known as Ensho no Yakata, in Suganuma village. The museum is located in a gassho-zukuri house that has been remodeled to showcase the materials and tools used in the production of saltpeter. Visitors can also learn more about the history of guns and gunpowder production in Japan, which date back to the Portuguese in 1542.
