Cut the grid paper to the size of the tiles. Line up the edge lines on the paper to the tile edges to maximize the grid space you have to work with when designing your invaders.
Stencil out the designs of the space invaders onto the grid paper. Include the invader's eyes in the designs as they break up the body's solid block of color. With their simple block designs, they should be easy to replicate on the paper.
Cut the designs out with the craft knife. Try not to rip either the core or the edge of the stencil design as both will be used to paint the tiles.
Clean the tiles and leave them in the sun to dry. The tiles must be completely dry before you begin painting on them.
Paint the tiles with the tile conditioner with the wide paintbrush and leave them to dry.
Line the hollow stencils up on the conditioned tiles surface. Using the sponge, paint the tiles. You want a clear edge to the invader so try not to move the stencil at all while dabbing the paint.
Allow the paint to dry. Layer the core stencil over the tile and paint on the eyes.
Apply a layer of enamel glaze to the tiles using the wide paintbrush. The glaze will protect the paint, essential of the tiles are going to be used as coasters or in the garden. Leave the tiles for 48 hours before using them.