The Book of Accounts was a record kept by Paolo Antonio Barbieri, Guercino’s brother, starting from 1629. Paolo Antonio noted the workshop’s income and outgoings in the register: the materials used, dates, clients, iconographic subjects and prices for all the works created by him and his brother. Guercino established the prices of the works starting from a fixed rate based on the number of characters in the composition and whether they were painted in half or full length.
The copies made by the workshop and the retouches by the master on those works of his that had already been delivered were also recorded in the Book. Each year ended with the total earnings and expenditure for the management of the home and the family.              
After Paolo Antonio’s sudden death in 1649, it was Guercino himself who filled in the records. From 1665, the master by then being too old, the accounting was assigned to his nephew Benedetto Gennari.

The last note written by the nephew in the Book of Accounts on the 22nd of December 1666 was not about the payment for a work but paid tribute to his uncle on the day of his death, thereby marking the epilogue of the Barbieri workshop.