The picture on the left shows a simple pinch form made from paperclay mixed with perlite. The amount of perlite used is just an estimate; enough to give some kind of texture. It survives the bisque fire without any problems. The form is extremely light. After sanding the outside surface of the form with a metal rasp, the random voids can be seen.
Compare this with the sphere on the right side (it's part of a sculpture I'm currently working on). It this piece, I used paperclay mixed with cooked rice. The mixture was applied as a thin coat (about 3/8" thick) over a bone dry paperclay sphere using paperclay slip as "glue." Many more regular shaped voids can been seen all over the bisqued surface of the sphere after sanding.
I was hoping to see more irregular voids from the perlite. I do see that some of the perlite still remains trapped in the bisque ware. I find the perlite from the bag is more varied in size, some ranging from size of coarse sands to around 1/4" in diameter.
I want to take both of these to high fire (cone 10 reduction) and am curious to see how the perlite behaves. I know how the paperclay mixed with cooked rice will behave as I have been using this technique for several years. I'll post another entry in the blog once I have completed this test.