Thanks for all of the replies.
I own the Shepard & Dietrich, and the fire assay book by Edward E Bugbee. They are both great books, and I have found them very usefull. I suspected speiss, or matte, but I was'nt quite sure how to identify it.
I usually run all of my assays at 2000 F, and I only assay ores for gold and silver. I have been using the sulfide ore flux from action mining, and I add flour for a reducing agent in different amounts, depending on the ore, it's usually around 2.5 g. My previous attemps at using potassium nitrate always ended up making the fusion boil over, so I have'nt used it since. The main ore I've been working with lately does have some arseneopyrite, but in very small amounts. I will try a low temp roast on the ore and see if that helps. Tomorrow I will see if I can find a large piece of slag in my bucket that I can take a picture of to show you what I'm talking about, hopefully that will show you better than I can explain it.
What kind of losses can I expect if speiss forms in my assay fusion? I guess the only way to know for sure is to adjust my methods to eliminate it, and compare the results.
I hope this better explains my problem, and I will try to post some pictures tommorow.
Thanks again,
rookieminer