Use syringe clay to decorate your unfired pieces. You can add lines, create little bezels to attach lab created stones and also use it as a slip to attach dry or wet pieces together.
Syringe clay also can be used on its own on cork clay to create filigree designs. Very simply, create a cork clay piece of any  shape you like and cover it with lines you extrude with the syringe. Fire it from a cold kiln to 650C for 30 minutes.