Unknown Woman's Portrait Found Beneath a Van Gogh Painting

Here's the link to the story of how modern technology reveals what's beneath the final version of a painting. In this case a portrait of a woman painted in mostly subdued browns and reds buried beneath the gorgeous light filled painting of blue, green and yellow grass in the painting we know as Patch of Grass, by Vincent Van Gogh. It seems that experts have suspected that there was some kind of portrait underneath and the new testing revealed the image. How did they know?? Sometimes ghost images of portions of paintings that have been painted over as the artists adjusts the composition, or complete paintings that have been obliterated by a new image, begin to show through over time as pigments in the paint become lighter and more transparent over time. It's called called pentimento, roughly, repentance, in Italian.