well look at you clay and start taking mental notes of of its visual properties.

- Is it shiny or dull - adjust the specularity to match
- Are the shiny spots pinpoints are spread - adjust diffuse
- Is it reflective - adjust reflectivity
etc...

Probably use a lambert or a blinn:
Lamberts = matte finish
Blinns = matte to gloss finish depending on settings

You can noise or variations in some channels with a fractal or noise texture.

Really recommend you just create a shader on sphere and play with the various channels/attributes until you get what you're looking for. In the process you'll probably get results that you can use for other material.

Just have fun with it.