An increase of 22 % in lead usage is expected in the European Union by 2050. The Harris process is a critical step during lead refining in which a salt melt is used to remove arsenic, tin and antimony. To further automate lead refining and improve safety, developing a reliable and replicable method to determine when the melt, known as the Harris slag, is saturated with impurities, and must be replaced is critical. To achieve this, a literature review of lead metallurgy focusing on the Harris process was executed. Antimony containing industrial Harris slag samples were collected and characterization was performed. Two different methods to determine the saturation of Harris slags were proposed relying on the viscosity and electrical conductivity of the slag. The physical fundamentals of the proposed techniques were discussed, and experimentally investigated using the industrial samples along with lab-prepared synthetic counterparts. Rheometric measurements displayed non-revisable time dependent behavior suggesting physical changes in the material when sheared casting doubt on viscosity as a reliable signal of antimony saturation. Contrastingly, electrical conductivity showed promise as it decreased with increasing antimony content. Recommendations are made herein to further develop the electroconductivity technique and address encountered issues.