Material

Glass
Mud in different colours
Sand in different shades

Method

First decide on how big you want your painting to be.
Depending upon the size get the glass cut at your local hardware store.
Once you have the appropriately sized glass sheets.
You can have a freehand composition or have one painted.
Depending on how you want your painting to look.
Depending on how you would like the patterns to emerge - use feathers, balls, strings and beads.
Get your cats to walk, run and jump with wet mud on their paws.
Once the mud is dry.
Apply varnish over the wet mud
For the remaining parts of your painting, apply a light coat of varnish or a suitable liquid adhesive and let the sand grains fall irregularly.
You can use a seive or let it fall naturally.
Allow to dry.
Congratulations! Your natural glass painting is ready! Jointly painted by you and your cat.
You can now frame your painting and call for your friends over to come and see your masterpiece!