They talk about it later on: > Similarly, silk was also used as a sacrificial object, such as in the form of silk books or paintings on silk, with the silk ser

They talk about it later on: > Similarly, silk was also used as a sacrificial object, such as in the form of silk books or paintings on silk, with the silk serving as a carrier to convey the content of the calligraphy and painting upon it to Heaven. But it does seem that there is some context that would be helpful here, at least for this Western reader.