Short answers, pulled from the story.
A thangka is a Tibetan Buddhist painting on cotton or silk, typically depicting a deity, scene, or mandala. Most thangkas were made for personal meditation or to instruct monastic students, while some large examples were displayed on monastery walls during religious festivals.
The word thangka means "thing that one unrolls" in Classical Tibetan. Thangkas are traditionally kept rolled up when not on display, mounted on a textile backing with a silk cover on the front.
The oldest surviving Tibetan paintings on cloth come from the Mogao Caves at Dunhuang in Gansu province, China. They were found in a sealed Library Cave that was walled off in the 11th century, with the Tibetan pieces believed to date from roughly 781-848 during Tang dynasty rule.
Thangka painting grew from the Newari Paubha tradition, and artists from Nepal were commissioned from the earliest period, bringing specifications for deity proportions and postures. The Nepalese artist Araniko, also known as Balbahu, became the chief Imperial artist of Kubilai Khan in the 13th century, extending Nepalese artistic influence into China.
Thangkas are painted on cotton or silk using a distemper technique, with mineral and organic pigments mixed in a water-soluble animal glue medium applied as a warm liquid. The composition follows a strict geometric grid, with each figure's posture, hand position, and features placed according to specifications drawn from Buddhist scripture. In Nepal, 24-carat gold is also plated over parts of some thangkas.
Most thangkas are comparable in size to a western half-length portrait, but giant festival thangkas designed for monastery walls can reach sixty or more feet across and twenty or more feet high. In Bhutan, these large festival examples are called thongdrels.