I enjoyed Nightmare in Wax, taking it on the pulpy level that it intends and achieves. It's fun. It's not mindlessly sadistic (so if you want that, look elsewhere). Not hopelessly incompetent, either (just a bit, maybe, but hope is there).
I admit that at first I confused it with a wax museum horror featuring a curator with a false hand, which is interchangeable with a hook or a cleaver. Were there two versions of this film? No; the man with the cleaver was Patrick O'Neal in Chamber of Horrors (1966). It gave me a restless night figuring that one out. These things worry horror fans.
The Patrick O'Neal film is a classier offering. The photography is much glossier, and Wilfred Hyde-White adds his own charm to the proceedings. But Cameron Mitchell in Nightmare in Wax adds his own special (if not too refined) touch of wickedness, pursuing Anne Helm through his Faustian workshop, hypodermic in hand. That chase between tottering dummies and bubbling vats doesn't quite elevate the film into the realms of horror achieved by Lionel Atwill and Fay Wray... but it's pretty good, all the same.
A couple of years before Nightmare in Wax, Cameron Mitchell starred in a Spanish/West German co-production of Island of the Doomed (1967) (a.k.a. The Bloodsuckers, The Maneater of Hydra, etc.) I was fortunate enough to see that sharing a double-bill with Slaughter of the Vampires. That was in my long-ago teens. Much more recently I bought it on DVD (with the widescreen sadly cropped). Now wouldn't it be great if someone had the discrimination (I shan't say the taste) to bring out a restored widescreen double-DVD of both Nightmare in Wax and Island of the Doomed. We can only hope!
