"Leaving the membrane" is done in a way similar to "engraving," just described. But when the membrane that is left is 80 % dry, a translucent solution is applied to protect it, and once exposed to light rays, it reveals the layers in shades of gray.
至於「留膜」，做法上和鏤空技法相同，只是在清理蛋內物後，留下蛋膜，待陰至八分乾時，塗上一層透明膠水保護，透過燈光投射，展現明暗層次分明的光影效果。