These three documents provide a remarkable story. Ashikaga Yoshiteru, a beleaguered Japanese shogun, had received a recipe for gunpowder from an allied warlord, named Otomo Sorin. This recipe came from the Portuguese, who first landed in Japan in 1542 and was transmitted to Uesugi Kenshin in 1559. It contains an optimal ratio of ingredients and explains how to make gunpowder into a slurry. What is interesting, however, is that this recipe was transmitted in such a way as to be readily readable by all, but the two letters, one by Yoshiteru and the other by Odachi Harumitsu, were carefully sealed. No one could open them without Kenshin knowing about it. These letters are, however, quite banal, and merely served as a way of verifying that this information was from the shogun. Odachi Harumitsu’s letter has similar precautions, but is overall less formal than the shogun’s letter, and treats Uesugi Kenshin with greater respect One can know how these records were folded and presented because the Uesugi documents were preserved in their original format, complete with the cover sheet, which is rarely preserved.
Images and permission provided by the Yonezawa shi Uesugi Hakubutsukan shiryokan
Ashikaga Yoshiteru wrote this document, called a gonaisho, to Uesugi Kenshin, an important ally, who in 1559 encamped at Sakamoto, to the east of Kyoto. Yoshiteru inquires about Kenshin’s health, and then states that a messenger, Ōdachi Saemon no suke (Teruuji) would provide Kenshin with information. This letter was sealed by what is called a kirifu. The right side of the paper was cut and used to tie the document. It was then covered in a second sheet of paper, called a kasanegami, which was folded and sealed with a line of ink. Finally another envelope, called a fushi, was used to enclose the document. This letter from Yoshiteru could only be opened by Kenshin, and the double seals ensured that no one else could see the contents of this record. The Uesugi documents are preserved in their original format, and it is rare to see such records in their original form.
This letter from Ōdachi Harumitsu explains the contents of the shogun’s letter. First Harumitsu too inquires about Kenshin’s illness. Next, he explains that Ōdachi Teruuji would be the messenger, who would bring the shogun’s letter and a gunpowder recipe, which the Ashikaga shogun had received from Ōtomo Sōrin, an important lord from Kyushu, who had considerable contact with the Portuguese. This document too shows sign of a kirifu, and so could only have been seen by Kenshin. It is of a form called a kirigami, where the original page of a document was cut in half, and in this case reflects Harumitsu’s lower status than the shogun, who dispatched a full sized document. Kenshin’s name appears higher on the page than the shogun’s letter which constitutes a sign of greater respect. Taken together, both of these documents functioned as a certificate that verified that the gunpowder recipe had actually been dispatched by the shogun.
This gunpowder recipe was transmitted from the Portuguese to Ōtomo Sōrin, who in turn informed Ashikaga Yoshiteru, who then bestowed it to Uesugi Kenshin. In contrast to the previous documents, which were secret in that they could only be opened by Kenshin, this recipe had no such protections. This document reveals that a sophisticated recipe could be transmitted from the Portuguese to the Japanese. The composition of gunpowder determined the power of an explosion and the distance that a bullet could be fired. Potassium nitrate, or saltpeter, provided the explosive potential, while sulfur lowered the ignition temperature, and carbon binded the other two ingredients. John Bate in 1634 characterized the ingredients as “The Saltpeter is the Soule, the Sulphur the Life, and the Coales the Body of it.” Early Chinese gunpowder recipes only contained 50-55% saltpeter, but in fifteenth century Europe, the ideal ratio of gunpowder was determined by the German general staff in the nineteenth century to be either 74:10:16 or 74:12:13 saltpeter to sulfur to coal. This recipe contains two options of 80:12:8 and 77:13:10, which closely approximates the ideal ratio. It also describes how to heat and mix the ingredients into a slurry, and dried, which was more effective than simply mixing the grains. Kenshin, after receiving this recipe, engaged in a series of attacks on his rivals, occupying Kamakura itself in 1560-61, and used guns effectively at the battle of Kawanakajima in 1562.