After the bisque fire, I sanded the sides to expose the voids. No glazes or oxides were used on the surface of the test piece. It was fired to Cone 10 reduction. The warm toasty color is the natural color of this manufacturer's paperclay (IMCO).
In this piece, you can see the melted perlite in the voids better (about 1/2" off the base near the right edge).
For some applications, this may be an interesting texture to have.