https://phys.org/news/2018-06-invisible-archaeological-elements.html

Mercedes Farjas, Aroa Gutiérrez and José Antonio Domínguez started by studying a limestone mold in the lab. The first goal was to assess the influence of the angle of the light of the photographs.

Later, after studying the effect of diverse filters on the mold, the researchers carried out combination tests of the filters in order to create a protocol of sequential application that allowed them to obtain conclusive results. As a result of these tests, they selected a set of filters and established an order of application.