Covering silver wire for use as a speaker cable

Willoamp, What about using both silver and copper wire?
This would increase the gauge .

Silver and copper ...

http://www.ultimatecables.com/

Also happens to be why I wouldn't bother making speaker cables.

Why would you be contemplating using silver and copper? If you can afford it, use silver only. It has the highest conductivity.

Willoamp, The silver wire I have is about 26 gauge.
The thought of using copper was to be able to add more gauge.

Here's a basic "rule of thumb" for estimating wire gauge needed when combining gauges. There's a chart for this somewhere.
Every time you double up the amount of silver, the effective wire gauge goes DOWN 3 steps.

If you double-up on 18 ga., the effective total gauge is now 15. Double up again (4 - 18 ga. wires), and it is now 12 ga. effective total.

Add two eight ga. wires together, and it becomes 5 ga. effective total.

So in your case, doubling two 26-gauge wires is now 23 guage. Four runs of 26 guage would now be 20 gauge, and so forth...