Fresco and wall painting
"Obviously the first problem faced by experts (archaeologists, technicians, and art scholars) has been the painting technique used in the Pompeian wall paintings. [...] Mengs, after a long and detailed study of the paintings of Pompeii and Herculaneum, concluded that such paintings could not be but frescoes painted with buon fresco by painters who had to have a unique skill and speed of execution. Requeno, on the other hand, claimed that Pompeian paintings were done with encaustic. Scholars' opinions were divided: some joined that of Mengs (Wiegman, John, etc.), others, that of Requeno (Donner, and Henry Cros, etc.). Many were the opinions and statements by other scholars: some considered them to be tempera (Carcani, Winkelmann, Schafthäult, etc.); others with backgrounds done with fresco and figures and decorations with tempera (Overbeck, Müller, Letronne, Woltmann, Mau, Gusman, etc.); resin-based paint (Knierin, etc.); milk-and-beeswax-based paint (Geiger); dry fresco (Eastlake); paintings done with several methods and mixed media (Berger, Raehlmann, Laurie); mixed media with overlay of wax; oil paintings; etc. [...] The chemical studies conducted by different researchers [...] have yielded uncertain and incomplete results, most of them contradictory". Selim Augusti. La tecnica dell'antica pittura parietale pompeiana. Pompeiana, Studi per il 2° Centenario degli Scavi di Pompei. 1950, 313-314.
"The determination of Roman [wall] painting technique has long being controversial and often passionate, sometimes led by imagination rather than critical thinking, hardly five years go by without an enthusiast being convinced of having unraveled the mystery of the Pompeiian painting”. Paul Philippot, Paolo Mora. Technique et conservation des Peintures Murales. Centre International d’Études pour la conservation des Biens Culturels et Comité de l’ICOM, sept. 1965, 1. 10.