The bench sweeps must be burned out before being melted.  In this way things like brushes, sanding disks, shellac, etc. that would hinder a melt and displace the precious metals into the slag that floats to the top of the melt are reduced to a carbon ash which then will flux off into the slag allowing the metals to melt into the bar.  Here the bench sweeps are put on a layer of paper in the burnout pan.  The paper causes a carbon layer to form between the sweeps and the pan keeping anything from sticking to the pan.

Here the bench sweeps are being burnt.

Here are the bench sweeps after they have been burnt.

They are demagnetized to remove mostly iron based material that would not melt properly and thus not allow for an accurate assay.

Bench sweeps typically contain a large percentage of non-metal, mostly carbon based material.  In the melting process the metal needs to efficiently separate from the this extraneous material.  To facilitate this a flux (borax) is added. 

To further assure a good melt an oxidizing agent (soda ash) is added to help oxidize any remaining organics and assure that they will not interfere and be fluxed off into the borax.

Once everything has been added and melted, it is stirred to assure the melt is complete and homogeneous.

Once completely melted and sampled, it is poured into a form.

The bar after pouring, cooling in the form.

The bar on the melt table after removal from the form.  A thick layer of slag is visible on the bottom (the bar having been flipped over in the process of removal from the form) that comes from a mixture of the flux and extraneous material.

The bar with slag being put into a bath of water to cool.