herbamatic said:
Hello all,
Just wondering what is the most commonly used crucible type for lead fire collection of gold? (not full fire assay, just the collection part with some other finish like AAS). fire clay, porcelain, corundum etc.
Also, is there a large difference in lifespan of the crucibles?
Thanks
Hi Herb:
Fire clay crucibles are used almost exclusively for the lead collection. They hold up well to the fluxes and molten metal, and are relatively inexpensive. There are various grades of crucibles, and will typically last for 3 to 6 uses. There are many sizes, which can be seen here (the are the AP Green brand, but there are several others):
[/url]www.lmine.com/category/ap_green_repack.html[/img]
The life will be less if you are not fluxing properly. For instance, if your flux is silica deficient, your melt will be too basic, your slag may be chalky, and have entrained lead. Silica will be robbed out of the crucible which will shorten the life. The fire assay text by Shepard & Dietrich is probably the best for understanding all the complexities of fluxing:
http://www.lmine.com/product/17202A.html You will learn to "read" the slag with practice, and can then make adjustments to your fluxing which will both improve your results but will also extend the life of your crucibles.