Lay the model's head back at a 45 degree angle. A reclining chair can help to minimize neck strain.
Apply a coat of petroleum jelly to the model's face. Coat particularly liberally along the hairline, eyebrows, eyelashes and around the nose. Plaster tends to stick, especially to hair, and petroleum jelly will allow the mask to release easily and prevent painful sticking.
Dip one length of plaster bandage into a 1-quart cup of cool water. Rub the strip lightly between your fingers to hydrate the plaster.
Apply the plaster bandage to the model's face lengthwise, just below the hairline. If the strip is too long, trim it with a pair of scissors. Smooth out any wrinkles and ensure that the entire strip is flush with the skin.
Add additional strips along the sides of the face and the jawline, forming the perimeter of the mask. Cut the bandages to fit the contours of the face, but leave the strips as long as possible.
Fill in the interior of the mask with bandages. Each bandage should overlap by approximately half an inch with the strips around it. Take particular care around the eyes and mouth, and leave openings in the plaster for the nostrils.
Add an additional two layers of bandages to the face, strengthening the mask. Allow the mask to dry for 5 minutes.
Gently pull the mask from the face, working from the edges in towards the center. Carefully slide your fingers under the bandages, and ask the model to flex and wrinkle his or her face to encourage the mask to release.
Turn a medium-sized bowl upside down and cover the top with clear cellophane. Lay the mask over the bowl to maintain its shape, and allow it to dry thoroughly for at least 48 hours.