Silver and gold alloys have been widely applied in the making of precious objects during the byzantine and post byzantine eras. A major category is the “ecclesiastical silver”, which was used in the celebration of the liturgy (chalices, disks, asterisks, blessing and benediction crosses, processional crosses, liturgical fans, wedding crowns etc.). This study focuses on post-byzantine ecclesiastical silver chalices, kept in parish churches and monasteries of Eastern Thessaly. They have been studied with non-destructive analysis technique (XRF) for the clarification of the role of gold (Au) in the Silver – Copper – Gold alloy. The main question answered in this work is whether gold (Au) was part of the compositional alloy or decorative and moreover if it was applied with amalgamation procedure (Au - Hg alloy). By using X-Ray fluorescence spectroscopy, mathematic procedures for data processing it is proved that in all cases gold was decorative and applied with fire gilding amalgamation process. Thus, in this work, it is proved that “fire mercury process” was the primary procedure for gilding ecclesiastical silver in Eastern Thessaly in the post-byzantine period.