Measure the diameter and height of your drum shade using the fabric tape. Add 1/2 inch to the diameter, and subtract 1/4 inch from the height. Cut the vellum to your adjusted dimensions.
Lay a leaf on the vellum and gently trace its shape onto the paper with your pencil. Place another leaf near your first outline and trace it as well. Continue tracing leaves all over the vellum, allowing at least 1/3 inch between shapes. Avoid overlapping your outlines or going over the edges of the paper.
Cut the leaf shapes out of the paper using a craft knife. Use a sharp blade to prevent the paper from tearing. Set your cutouts to the side.
Roll the vellum gently to form a loose tube. Place the tube inside your drum shade. Allow the vellum to unroll and expand until it rests against the interior of the shade.
Adhere the top and bottom corners of one edge of your vellum to the interior of the shade, using glue dots. Attach the paper with glue dots every 2 or 3 inches along the top and bottom rims of the shade. The vellum will overlap approximately 1/2 inch at the seam.
Affix the leaf cutouts to the exterior of the shade with glue dots. Overlap the interior vellum silhouettes slightly to create a natural falling leaves effect. Just a few scattered leaves or large clusters may be added, depending on your preference.
Attach the updated shade to your pendant lamp.