In the fire assay speiss is usually a combination of Fe & As. Speiss is formed when the iron method is used on ores containing arsenic. It is a hard, fairly tough, tin-white substance found on the top of the lead. If a small amount of arsenic is present, the speiss will form a little button on the top of the lead. If there is lot arsenic is present, the speiss may cover the entire top of the lead. Speiss contains Au & Ag, and may be cupelled along with the lead if there is less than a gram of speiss. Larger amounts are difficult to deal with and the sample should be assayed by another method.