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
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.
"If you love your job, you'll never work another day in your life."