Different string wrappings.
There are three different Spirocore C Strings, Silver, Chrome, and Tungsten wound. Can anyone clarify the difference. Between the tone of the three? The tension is the same on all three.
From my experience on violin silver compared to aluminum ends up being a skinnier string with a warmer tone usually.
Speaking for cellists: the density of tungsten (W = "Wolfram") is almost twice that of silver so you get a thinner, more responsive string with tungsten. I prefer the Spirocore tungsten C string to most I have tried. Of course the tungsten strings are more expensive. I have not liked the chrome wound strings.
These are generalizations from trying these on a few different violas...