I really like the idea of intricate clay designs embedded in clay. Not having the ability for a truly artistic attempt, I've begun to rely on rubber stamps to give me that look with little effort. Here is how I make inlay designs using rubber stamps. A more detailed tutorial is located on Instructables.com.
Roll your clay to a uniform depth using a clay pasta machine. I like to use the thickest setting for this.
Dust your rubber stamp* with a light coating of corn starch, removing the excess with a dry paint brush or cosmetic brush. I use corn starch because it dissolves in water and washes away easily.
Press the stamp uniformly into the clay. Make sure the top surface is still smooth and that the piece is a uniform thickness. (If not, run it carefully through your pasta machine again to smooth down the top.) Trim around the design as desired.
Bake the clay according to package instructions. When the clay is cool, rinse it off with cold water to clean off the corn starch. Make sure the clay is very dry before moving on.
Press the contrasting inlay color of clay into the design. Press down from the top and push out any voids.
Remove as much clay from the top as possible. Use your clay cutter to scrape off excess clay. Any clay not removed here will be manually sanded away. (I’ve had a modest amount of success removing excess clay by running the piece through the pasta maker again. I haven’t had enough success to fully recommend it.)
Rebake your piece to solidify the inlay. Once it is cool, use waterproof sandpaper and soapy water to sand away any excess clay from the top. Pay attention to the design, rinsing as you go and only sanding where it is necessary. It is possible to use progressively finer grades of sandpaper to create a glossy finish. However, I prefer to glaze over the top when the piece is finished.
* Not all rubber stamps are going to give a good inlay image and, the inlay design may not be as detailed as the stamped image. Test your image on some scrap clay and look carefully at the shapes in the smooth top surface of your clay as that will be the design of the inlay—not the deeply set detailed design that normally appears when it is used as a stamp.