Separating / Removing Slag from the Gold rich Lead Button

When the slag is cooled, the slag is separated from the Pb button by pounding it off with a hammer and then cubing the Pb button so it can be easily picked up. The lead button should be bright, it should separate from the slag easily and there should be no evidence of matte or speiss on the top surface of the button. The Pb buttons should be between 15 to 35 grams. One should keep a record of past sample fluxing history as to change and improve on the fluxing of difficult samples. This can help to attain correct button size, poor slag/ button separation, matte or speiss and other problems. After the fusion material is poured into mould and cooled, the lead button is separated from the slag by hammering the slag off the button.

There are two undesirable products matte and speiss that are occasionally obtained. There can be a third product if salt is used or if nitre is used in the assay. The third product will be found on the top of the solidified slag. 

Matte is an artificial sulphide of metals found in the ore and /or flux.
It is formed in the nitre fusion of sulphide ore when the charge is too acid.
It is found just above the lead button. It may be quite thick, or it may appear simply as a granular coating on the upper surface of the lead button. It is usually blue- grey in colour, resembles galena and is very brittle. The matte always carries some of the gold and silver. It is usually broken off and lost in the slag during deslagging of the lead button leading to low results. If it occurs, the assay must be repeated with more basic fluxes and less acid fluxes.

Lead shot in the slag: This is usually caused by the temperature being too low or too little silica in the charge. Should shooting occur, increase the amount of silica and litharge and re-fuse at a higher temperature.