Wearing latex gloves, use a craft brush to apply a thick layer of etching cream over your stencil, being sure to cover all of the exposed mirror. Brush first with up-and-down strokes, then go side to side to ensure even coverage. Allow the etching cream to remain on the mirror for at least 10 minutes. Take the mirror to the sink, and wash under running water. Peel off the remaining adhesive paper, and clean the mirror using window cleaner. You’re done!