For a visible glow from this mostly etched design, you'll need to remove enough of the pumpkin rind to make the remaining layer translucent without puncturing completely through the side of the gourd. An easy way to gauge your progress is to shine a small flashlight at your etched design from inside the pumpkin. If you see a glow from within, you've etched deeply enough!
1. To clean your pumpkin, slice a circle in its bottom (not its top) and pry it out with your knife. Reach in to remove the pumpkin innards, reserving seeds to toast as a snack, if desired. Scrape the pumpkin's interior walls clean and scrape the pumpkin thinnest on the side you're planning to carve. (About 1" thickness is ideal.) Level the pumpkin circle with a knife to create a flat surface for resting a candle.
2. Affix the printed art nouveau leaf pattern to the side of your cleaned pumpkin, smoothing the pattern down with your hands and securing it with clear tape. Pierce along the stencil lines with a pin tool, outlining the design with closely spaced pin holes. Remove the stencil, but keep it nearby for reference.
3. Find areas on the stencil that are surrounded by dotted lines; etch these areas with a gouge or sharp crafts knife by peeling off the pumpkin skin. Be careful not to puncture through the pumpkin wall while etching.
4. Find areas on the stencil that are surrounded by solid lines; carve these areas with a serrated woodcutting or specialty pumpkin-carving knife.
5. Wipe carved and etched surfaces with petroleum jelly to seal in moisture. Place a battery-operated candle on the prepared pumpkin circle and set your carved art nouveau leaf pumpkin over it.