The painting was a fresco. There are a few ways to make frescos but the one employed here was likely buono fresco: colored pigment applied directly to wet plast

The painting was a fresco. There are a few ways to make frescos but the one employed here was likely buono fresco: colored pigment applied directly to wet plaster. In this way the painting becomes a physical part of the wall. In contrast, an oil painting is typically a thin layer of paint applied on top of another layer of paint on top of fabric. Though this way of painting is ridiculously long lived, it is very difficult to work with. The plaster dries so quickly that the painting has to be done is small chunks, like a jigsaw puzzle. There is also very little room for correction.