Part of hard gold jewelry turns black after burning,and the black position does not change after wiping.In light of the phenomenon,metallographic microscope,X-ray fluorescence spectrometry,and inductively coupled plasma emission spectrometry were used to analyze the black part qualitatively and quantitatively with the help of the analysis of the electroforming process.The test results show that the black material element is mainly Cu,and contains trace elements such as Zn,Mg,Al,etc.Cu is oxidized at high temperatures,generating black materials.The principle in which hard gold jewelry is made is the electrodeposition process.In the process of core removal,the local conductive layer (copper coating) is not cleaned thoroughly,and oxidized and blackened at high temperatures.