# Modulation of the S/HgCl2 Ratio for the Synthesis and Conversion of Cinnabar and Metacinnabar

## TL;DR

This study explores how to synthesize and convert cinnabar and metacinnabar by adjusting the sulfur-to-mercury ratio, which is important for preserving historical artworks.

## Contribution

The paper introduces a novel method for synthesizing and converting α-HgS and β-HgS by modulating the S/HgCl2 ratio.

## Key findings

- Spherical β-HgS-1.2 showed distinct morphology compared to α-HgS-1.0 and α-HgS-1.5.
- Adding sulfur or HgCl2 successfully converted black β-HgS to α-HgS.
- XPS and ICP-MS provided insights into the elemental composition of HgS.

## Abstract

Cinnabar has been used as a red pigment for centuries, but its degradation significantly impacts the aesthetic quality of historical paintings, particularly murals. Therefore, investigating the preparation method and transformation process of HgS is highly significant for mural research. In this study, we compared different sulfur sources for HgS synthesis and precisely synthesized α-HgS and β-HgS by adjusting the S/HgCl2 ratio. SEM and XRD analyses under optimal conditions demonstrated that spherical β-HgS-1.2 exhibited significant morphological differences in comparison with α-HgS-1.0 and α-HgS-1.5. Elemental analysis of HgS was conducted using XPS and ICP-MS for qualitative and quantitative insights. Based on the potential mechanism of cinnabar discoloration, two strategies for converting black β-HgS to α-HgS were proposed and successfully implemented by adding sulfur or HgCl2.