In the early modern age Japan was a kingdom rich in metal resources. A lot of gold, silver and copper were produced and exported to foreign countries, nevertheless Japan maintained a national isolation policy. The Iwami silver mine located in Shimane prefecture was the representative silver mine that prospered most. It produced about 10 % of the world's silver output. It is now mostly abandoned and reduced to ruins. Only a famous picture scroll remains to indicate its real activities. Through archaeological excavation started in 1983, it is becoming clear that extensive remains of mining and smelting are preserved. From 1996 scientific investigation of the excavated remains has been conducted. During excavation, and confirmed by scientific research, we recognized that the artifacts deposited during both the mining of the silver ore and the smelting process could be classified into two artifactual types; objects and fragments produced in the dressing process that were not influenced by a heating process and objects influenced by a heating process and produced by smelting and refining. The low grade ore, waste and tailings (remains after gravity concentration) that were scrapped in the dressing process are included in the former type, and the furnace fragments for smelting and refining, tuyeres (blast pipes) and slag and other smelter remains are of the latter type. The waste and tailings scrapped in the dressing process have not previously been studied. This study aimed at systematically investigating the dressing technology and estimating the ore grade through the evaluation of the range of variation in the waste and tailings left as scrap in the dressing process. The analytical results revealed the actual activities practiced at the Iwami silver mine in the dressing process.