Mold reversal is a technical method in special effect makeup, which aims to design and create the shapes of characters in stories, close to the needs of characters, and change the external image of actors through mold reversal technology. Inverted mold is a kind of prosthesis made of glue or foam material, which is made according to the face of the person to be placed on the mold. Through these artificial limbs, real people can reduce the requirements for CG special effects and make the scene shooting more realistic. In the common Star Wars, all kinds of aliens are not characters produced by key, but real actors who achieve realistic special effects through reverse molding.

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Inverted mold usually covers the parts that need to be inverted with alginate, such as face and neck. Professional die casting is completely operated on the basis of safety, whether it is material or process. However, some nonstandard operation methods, such as someone touching the skin directly to take the mold, may cause the plaster to stick to the actor's hair or cause the plaster to be allergic. Alginate is an extract of seaweed, which can be eaten (of course, it can not be eaten and can be used to take dental casts). Therefore, it is not dangerous to find a formal team or company to operate the inverted mold. As for the claustrophobia of actors mentioned by some people on the Internet, it generally does not appear.