Songfacts®:

• This song is about a Chicago groupie known as Cynthia Plaster Caster. When they were assigned an art project at the University of Illinois to plaster cast "something solid that could retain its shape," Cynthia and her friends Dianne and Marilyn came up with a clever way to get backstage and have a unique interaction with band members (or band's members): they would made molds of their penises in plaster of paris.
  
  Carrying around an official looking "kit," their plan worked and they succeeded in making casts for many musicians and their associates, most notably Jimi Hendrix, who had an exceptionally large cast. The Plaster Casters are discussed in detail in a chapter on groupies in Jerry Hopkins' book The Rock Story. Cynthia died on April 21, 2022, at age 74. >>>

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• How did Cynthia Plaster Caster feel about this song? Here's what she told Songfacts in 2014:
  
  "When someone first alerted me to the song 'Plaster Caster,' I wasn't too thrilled. It seemed like Gene Simmons wrote the song to make people think that he'd been casted, which he most certainly never was. But years later when Evan Dando's band the Lemonheads covered it, I started to notice how catchy the melody was. Nowadays, I'm all right with the song. Don't LOVE it, but I like it. If it's changed my life, I'm not aware of it."
• The members of Kiss were never molded by Cynthia, but the band is notorious for their backstage activities with groupies. Gene Simmons is rumored to have a collection of Polaroids that would make Larry Flynt blush.
• Cynthia Plaster Caster is one of the greatest groupies of the golden era of groupies, which was the mid-'60s to the late '70s. Competition was fierce for the attention of rock stars, and Cynthia had a gimmick that made her so renown, musicians would seek her out. Beyond the gimmick, however, Cynthia was very astute: she worked in a team, doing most of her damage with her apprentice Dianne. She had a penchant for British acts, so she learned their dirty language, which got their attention: she knew that "rig," "chopper" and "Hampton wick" were all cockney slang for penis, so she would often open an encounter by asking, "how's your rig," then introduce her services. A master of marketing, she had business cards and T-shirts, branding her and Dianne "The Plaster Casters of Chicago." She was so successful that impostors came on the scene and started stealing her act, but boys in the band always wanted the real thing.
• Frank Zappa considered Cynthia a brilliant conceptual artist, and brought her to California. Zappa, who was introduced to the Casters by Eric Clapton, never got casted, but was always coming up with ideas for how they could present their art. The casts have been exhibited from time to time, but Zappa didn't live long enough to pull off his idea for a "Cock Rock" exhibit featuring the casts.