The decades of the 50s and 60s constitute the great age of fresco detachment–stacco and strappo are the techniques–and in 1968/69, the Met, together with the Florence Soprintendenza, organized the exhibition “The Great Age of Fresco” which traveled to London and Amsterdam after its NY debut.
War damage, frescoes exposed to the weather, threats of vandalism, and the Arno flooding were all good reasons for the detachment of frescoes. The finding of the sinopie and the ability to crate the works up, to make them portable, and show them around the world were other reasons. (The ancient Romans took murals from Greece as war booty and commonly moved frescoes around Italy.) Now, the practice is frowned upon and frescoes are only detached if they are in imminent danger. And, in truth, it is better to see them where they were created rather than some piece of masonite, looking forlorn, even if we can’t look at the sinopie.
The strappo method of fresco removal involves painting a layer of reversible glue onto the fresco surface and affixing a piece of cloth all over the fresco. Once the glue has dried, the cloth is carefully peeled from the wall, taking the painted surface with it. With the stacco method, the intonaco layer is taken with painted surface, again with glue and cloth. A knife is used to separate the intonaco plaster away from the coarser arriccio layer below. The arriccio is the layer where the sinopie were painted/drawn.
In 2007 I went to a fascinating lecture at the Frick and was very surprised to learn that the great drawings collector Pierre-Jean Mariette (1694 – 1774) used a similar method to split drawings in half. The lecture was given by Kristel Smentek, who wrote her dissertation on Mariette and is now a professor at MIT. Here is a link to a pdf with the slides from a lecture Smentek delivered. It shows drawings from Mariette’s collection, including an Albani drawing he split, and a conservator in the act of splitting a printed sheet in two. The recto and verso of the sheet are covered with glue and paper or cloth (looks like high tech conservation material) and then performing what looks like magic in making one piece of paper into two.
While I hadn’t heard of splitting drawings before Smentek’s lecture, it is not so uncommon. Josef Meder, the early 20th century curator and later director of the Albertina in Vienna, split drawings in that great collection.