Chinese Cinnabar Brooch

This is a Chinese Cinnabar brooch which belonged to my grandmother, and would have been bought overseas by her husband in the 1920s-40s. It's just over 2" long and pretty chunky. It appears to be silver plated, with what looks like brass underneath, and is stamped "CHINA" on the back. This would confirm that it is likely to be silver plated brass according to this website:
http://www.danaraejewelry.com/chinese-export-research.html
"Around 1920 there was a major increase in the amount of jewelry that was exported out of China for other markets...During this time silver jewelry was usually marked with CHINA SILVER, SILVER or SILVER MADE IN CHINA. Plated brass jewelry was usually marked CHINA. "