The process for jewelers sweeps assays is usually done on larger lots, although the lot size doesn't matter, small lots which will be processed in Aqua Regia are generally settled on out-turn. So a fire assay isn't even done. Larger lots are generally fire assayed and then accumulated and shipped to a smelter because their rates are quite appealing if your quantities justify.
When you acid refine sweeps, two things will happen. One, you will not recover the silver, it remains in with the undissolved as silver chloride. And two, you will leave behind some of the gold. I do work for a good number of refiners who process "residues" from smaller refiners who do process in acid. Their assays are usually high in silver and average 1/4 of 1% gold. So it seems that the small guys acid refining are not getting all of the gold either. I am quite sure that some of the more careful acid sweeps refiners get more of the gold (like the guys who learned here!) and there are some who leave more behind in the residues. But on average there is 1/4 of 1% remaining after refining. The customer does not get paid for this because the acid refiner didn't recover it but the acid refiner gets paid for it when he accumulates enough residues to send out.
So some would ask, if I have to send it out anyway to get paid for everything why don't I fire assay it and accumulate it and get paid for it all without bothering with the acid refining? The answer, at least in the USA where the jewelry manufacturing has diminished significantly, is it will take so long to accumulate enough sweeps to ship out that you may lose all of your profits before you ship. (Of course you may make a lot of extra money too, depending on how the prices are moving but in recent years the bears have been in charge and the price has been falling. Where are the bulls when we need them?)
So refining for small lots, say incoming 20 pounds or less, acid refining is the method most used. After incineration, that 20 pounds will be about half the weight, or 10 pounds to put up in acid.
So the question becomes how many pounds will you be getting for processing? If it is a small quantity, you will pay on out-turn and will not be running a fire assay. But if your answer to the jeweler requires you say YES! with a big smile, we can go over the procedures here and you can learn and practice the techniques, and you will be capable of assaying the material. It just isn't needed to process in acid.
Honoring, if the assay turn to be 1% gold but when processing the main batch I get less. How is this handled.
Wow, I actually answered the question before I posted this response. The answer comes down to what we have been saying about refiners all along. To get and keep your customers your clients need to trust you. You will be picking up material that is un-incinerated from a jeweler The material cannot in any way be sampled in a way that guarantees it is homogeneous. So you have to incinerate it, crush and sift it and sample it before the customer even gets the assay. Generally a refiner has your material a few days before you get the results from the assay.
So if you have the material for a few days what are you supposed to do? Process and sample it, report it to the customer, and have them tell you it is too low give it back. (I'm from New York, that happens!)
If you incinerated, screened and processed in acid in the same few days, you will know the out turn, then you can do the math and tell them the percentage yield per pound, based on what you recovered, and you have honored your assay and don't have to wait for the gold.
