## 1 Historical and Technical Background  
The ancient city of Bagan (formerly called Pagan) is located in the Myanmar Mandalay Region of Burma. Between 1044 and 1287 AD, Pagan became the capital of the Pagan empire and grew into the political, economic and cultural nerve centre of the region. During the kingdom, along with the diffusion of Buddhism, a large number of religious buildings were built under the patronage of kings, nobles, and digitaries and of large sections of civil society, as attested by commemorative inscriptions [1].  
The remains of about 10,000 pagodas, stupas, temples and monasteries still stand today on the Bagan plains (Figure 1a), which cover an area of 104 square kilometres, outlining the landscape of this unique site [2].  
The temple is the most common architectural type in Pagan that become an autonomous structure with respect to the monastery since the 11 th century. Characterised by a central plan, and longitudinal or cruciform in design [1], most temples are built with fired bricks joined with mortar, while whitish stuccoes partially covered their facades [3]. Interior walls and vaults are decorated with wall paintings, many of which dated from the 11 th to the 13 th century. These wall paintings are characterised by vivid colours and black, brown or red outline drawings. A figurative repertoire is generally taken from the former lives of the [PERSON]; decorative friezes with plant motifs and geometric patterns were also largely used.  
Plaster's constitutive materials range depending on the chronology: mud, lime, sand with glue and jaggery (plant-derived sugar) were used in an earlier period (11 th-12 th century) while sand and lime were more commonly utilised in the later periods (from the 13 th to 16 th century) [4; 5]. The plasters were composed of one or more layers and usually, a thin primer of slaked lime was applied [6; 7]. Carbon black or red ochre was sometimes used for the preparatory drawings [8; 9].  
Pagan wall paintings were generally executed with _a secco_ technique and coated with a protective varnish made out of gums or resins. Natural gums including acacia [7] or Neem tree gums [6; 10] were usually used as binders. Materials and executive techniques employed over the centuries in Pagan has been introduced to Burma from India, evolving in a different expression and style [10]. Indeed, the knowledge of the Indian technique of  
Figure 1: **(a)** Me-taw-ya temple (1205); **(b)** Me-taw-ya map by [PERSON] inventory with XRF investigated areas; **(c)** interior, detail of the circle pattern with lotus rosacea motif; **(d)** Eastern vestibule, north-east wall, detail of XRF investigated areas.  
wall painting is useful to understand the painting technique in Central Asia. As a binding medium, beeswax and glue were used in the Buddhist wall paintings dating from the 2 nd to the 7 th century. Glues are produced by vegetable materials (gums, pulps and saps of different plants and trees) or using animal derivatives (gelatine produced by boiling buffalo skins) [4].  
The earliest reference to the use of colours and pigments, such as vermilion, red lakes, and natural ochre can be traced to the Sawhlawun inscription datable to Sakaraj-598 (1236 AD) [6]. Orpiment, carbon and bone black have been detected thanks to previous investigations [8,11]. Blue and green pigments are rare in wall paintings from the first period; greenish tones are usually obtained by mixing orpiment and bone black as in the Pahtothamya temple [6]. Conversely, in the later period, copper-based greens were in use [8].