Protect your hair and clothes from rogue plaster. Put on some old clothes to keep from getting plaster of Paris on any clothing you like. Long hair should be tied out of the way or secured in a shower cap to keep it out of the plaster.
Spread a thick layer of petroleum jelly on your lips, face and in any area you think might have contact with the plaster. This will help you remove the plaster when it has dried.
Mix a plaster mixture consisting of two parts plaster of Paris to one part water.
Apply the plaster with the help of a partner. The person whose lips are being molded should lie down in a position that will be comfortable as the plaster dries. Spread the plaster gently over the lips in an even fashion.
Go over the coat to check for smoothness and fill in any thin spots with more plaster.
Wait 20 minutes for the plaster to set.
Remove the plaster. Removing the plaster is easiest if the subject sits upright and wiggles her facial muscles as the mold is gently pulled from her lips.