[Kumabjorn]

I suppose this might have been a tad esoteric.
The answer is mid to late 8th century, known as the Nara period in Japanese history. The prints are known as the Million Pagodas with Dharina Prayers. They were a gift from the empress Shotoku to all the newly established Buddhist temples. The volume of the prints suggest that metal casting was used.
Paul was closest with them being prayers, take it away.