More and more assay laboratories are using flux made with bismuth oxide rather than lead oxide (litharge). There are a variety of reasons to do this. Bismuth is more environmentally friendly, so disposal and recycling are easier. Bismuth is also has less exposure risk. We always recommend wearing proper respirator protection as bismuth flux contains silica, but blood-lead monitoring is not needed and the medical surveillance is less rigorous. This does raise the question of the best type of inquart. Traditionally, inquarts (such as the Herman Inquart) have been a silver lead alloy. It seems counter-intuitive to add lead into the bismuth flux assay. There are two alternatives: 1) You can use a pure silver inquart. However, for the smaller inquart weights (like 2 mg or 4 mg) the inquart is made from very fine wire which can be difficult to handle. 2) You can use a silver copper inquart. These are larger and easier to handle, similar to the silver lead inquarts. But they do not contain lead so will not introduce lead into the bismuth assay. Currently these are available in 2 mg and 4 mg silver weights and further details and pictures can be seen here: http://www.lmine.com/category/copper_silver.html