Although the Chinese didn’t immediately think of it as a writing material (preferring split bamboo for everyday use, and silk for high-status texts) paper found a multitude of applications across the Chinese empire while the codex spread across the Roman Mediterranean and Near East.

These abstract concepts were expressed with new bookkeeping techniques: accounts had two sections, debit and credit, and each transaction was therefore entered twice, once on the debit side, once on the credit; ample cross references connected different customer or commodity accounts; a final financial result was summed out of the combined income;

Back in 1299, the Tuscans had one such unfair advantage: their bookkeeping. Florence’s merchant banks prospered because they were better at business than anyone else.

To conjure the devil, play a C and an F# together, or listen to the intro to Jimi Hendrix’s ‘Purple Haze’.

Paper supplanted papyrus, having ‘a transformative effect’, as Jonathan Bloom, the leading historian of the subject, puts it. For the following four centuries, Persian, Arabic and other Muslim intellectuals raced ahead of their rivals and counterparts in Christian Europe.

Historian Jacob Soll makes a powerful claim: ‘Without double-entry accounting, neither modern capitalism nor the modern state could exist.’ When I spoke to another historian of the period, the paper specialist Orietta Da Rold, she needed only two words to evoke this intersection of conceptual innovation, advanced manufacture, information technology

Hockney’s telling point is that it is not enough merely to look at a work: if an artist wants to learn from it, they need to make their own record of it, and in doing so, come to fathom it better. This is how art lives and grows.

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Sentimentality may provide the answer. This tatty, scarred, yet practical notebook must have acquired value as it passed from hand to hand, accreting knowledge and nuance as it went. The constant companion of a succession of childless Franciscans, living and dying together in the community of their order, perhaps it came to embody the bonds that gr