Copy via pricking

Look closely at this image (right-click > view image) and you’ll see that the main lines have been traced by pricking holes around the edges. A thin sheet underneath would receive the prickings and could serve as a stencil for making numerous copies.

Vies de saints.
Source: gallica.bnf.fr

Bibliothèque nationale de France, Département des manuscrits, Latin 11751, fol. 59r