Highly Polished wire????

That is a great point. If you use sand paper you are going to leave minute traces of Aluminum Oxide on the wire. I would suggest cleaning it afterward with water and a mild detergent. Just be sure to dry it very well to stop corrosion.

I use to prep the surface of copper, zinc, brass, and magnesium. We would grind the surface because impurities have a tendency to rise to the surface when casting and rolling the metal. We needed an ultra pure surface so the plates could be used in photo etching. Any and I mean any impurtities or foriegn material that was left on the surface would screw the etch up.

We used silcon carbine and aluminum oxide sanding belts and we use to have to grind with oil because of the flamability of magnesium. We would then clean the surface with water spaying out of jets and a mild detergent. To much detergent would contaminate the surface and too little would not clean the oil off.

I have cast zinc by pouring it in a mold and I have cast tantilin and tungston by casting in a vacuume. The methods used has a huge effect of the purity and the characteristic of the metal. You also can trap other impurities like carbon and oxygen during the casting process.

The tantilin was for compacitors and all the metal I have worked with was always actually a mix of metals. This gave it its best electrical or etching qualities. It might only be one percent zinc in the copper but this all makes a huge difference.

I worked with one of the world leading companies that produced semi conducters for capacitors. I personally worked on and ran the vacuume chamber, computer system, and electron beams that cast the metal and removed the impurites.

It used four electron beams that would melt the metal. This was done at such a high tempature that it would vaporize all the impurities and then the vacuume chamber would pull them away while they were in gas form.

The vacuume chamber and electron beams alone were a 60 million dollar set up. That doesnt include the room full of tranformers, the targeting system in which to control the electron beams, or the all the other equipment that filled the room to support this system. I was told that we had one of the most advanced systems in the world.

Our purity didnt get close to what is claimed above. You have to understand that they system used to remove the impurities also, in a small degree, adds other into it. If we melted to quickly you would get an excess build up of oxygen and carbon and could never fully remove them from the metal.

I would be very interested to know what casting process is used to make the silver for silver wire.

As far as sanding goes there are a few things to take into consideration when determining roughness. The grit is how many particles per square inch but theres more to it then that. The backing is just as important. A cloth backing is much rougher then a paper backing. It also depends on the shape of the particle and what the particle is made out of.

For something as soft as silver I would recommend steel wool over sand paper. Maybe a very fine steel wool. Dont let the name fool you a very fine steel wool is finer then most sandpaper.

One thing that you have to understand about sanding is that everything is an abrasive. Even a soft piece of polyester its just the degree in which it does it.

Acetone as mentioned above is also a fantastic suggestion and I would think in most cases better then sandpaper.