Erik Kwakkel’s blog medievalbooks has an informative post on the design and layout of medieval manuscript books, entitled Architecture of the Medieval Page. When you are looking at a richly illuminated book you have narrow your eyes to detect behind the text and illustrations surviving evidence of the indentations of the grid pattern the scribe would start off by ruling into the surface of the parchment. Later on a lead “pencil” would be used and these lines might subsequently be erased.

The grid pattern is especially obvious in these examples.

This is sort of like that ruled sheet you used to get in a pad of Basildon Bond letter-writing paper. If you stuck one of these behind a sheet of parchment though you wouldn’t be able to see through to it. I am in fact using just such a ruled sheet from my insane handwritten version of The Dynasts. (Not as much progress as should have been has been made on this since my last update. I took the last winter off for one reason or another. This has to be a seasonal activity: I don’t know if scribes were troubled by drops of sweat from their brows — but this is obviously incompatible with pen and ink production. Thus activity has to stop during the humid summer months in New York. I think it should be safe to start up again now.)