Special effects artists are a bit like magicians: they can use the most innocent-seeming of everyday objects to create an illusion that, even though we know it’s not real, can still make us believe.

Special effects co-ordinator Dan Martin is an expert in all things gruesome and gory, having worked on horror films including The Human Centipede II, The Devil’s Business, and F. His studio, 13 Finger FX, is currently working on effects for the new film by Ben Wheatley, director of Kill List.

Here, he talks us through some of the most common effects used in the movies, and gives us some tips for a killer Halloween costume…

Severed legs
As seen in: Severance
What it’s made of: Silicone with a fiberglass core
How to make it: Making fake limbs requires a series of moulds to be made. First, a cast is taken of the actor’s leg.

“You cover their skin in moisturiser, and then coat their leg in alginate – which is the stuff dentists use for making moulds of teeth,” Dan explains. The alginate isn’t strong enough to hold its shape, so a two-piece plaster bandage cast is put over the top.

This alginate and plaster mould is used to make a “master positive” – a recreation of the leg made from plaster or clay. Next, a fiberglass mould is made from the master positive, and then that mould is used to make the prop leg. The fibreglass is lined with clay and fibreglass is layered in.

“So when you remove the clay, you’ve got a mould and a solid core, and you pour silicone around that,” Dan says. “Then you take out the leg, clean it up, and paint it.”

Severed heads
As seen in: Hostel
What it’s made of: Silicone, fiberglass, and yak hair
How to make it: Making a prop severed head is similar to making a prop severed leg, with the added complication that you need to take a mould from a person’s head.

And beards present a particular challenge. “Anything that involves hair is time-consuming and horrible,” Dan says. To prevent the alginate getting stuck, moisturiser has to be caked on, filling up the gaps between the hairs.

“If they’ve got a beard, you use plastilene – a kind of posh Plasticine – to make the master positive, and then you need to sculpt their face to make it look like they’re clean shaven,” Dan says.

Then, when the final silicone version is created, the hairs have to be punched in, one at a time. “It’s usually yak hair we use for beards,” Dan says, “It’s nice and long.” Eyelashes and eyebrows also need to be individually punched.

Foam weapons
As seen in: Hatchet, My Bloody Valentine 3D, Human Centipede II (Full Sequence)
What it’s made of: Expanding polyurethane foam
How to make it: Most weapons in horror movies are actually soft, light replicas made of foam. “There are different kinds of foam – some set like marble, but there are lots of soft ones. If you were making an axe, you’d use a soft one,” Dan says.

To make a soft prop axe, a mould is taken from a real axe by half-burying it in clay, covering it with silicone and fibreglass, and then repeating the process with the other side of the axe. The polyurethane foam comes as a two-part liquid which is stirred together before being poured into the mould.

(For long weapons, like axes or crowbars, a rigid armature is also included inside the prop, to keep it from flopping around.)

After the foam has set, it’s removed from the mould and painted to look exactly like the real thing – just squishier.

Torn zombie faces
As seen in: Land of the Dead, The Walking Dead
What it’s made of: Fake teeth, silicone, and lots of make-up
How to make it: Many zombie movies have characters walking around with part of their faces torn off, teeth showing through – though, of course, the actors’ faces are intact underneath.

“To make it look like the teeth are showing through the cheek, you create a set of dentures which hook out of the actor’s mouth and sit outside their cheek,” Dan explains. While the actor is wearing these dentures, a cast is taken of their face and used to make a prosthetic for them to wear during the movie, made from foam latex or silicone.

Clever use of colour can also create the illusion that a face is caved in: “Your brain adjusts to see what it expects to see, so you can reverse paint the actor’s face and the eye will flip it; it’s almost like a trompe l’oeil effect,” Dan says.

Demons and other weird creatures
As seen in: Hellboy
What it’s made of: Foam latex, fiberglass, silicone… and lots of other stuff
How to make it: “You can do creature effects in one of two ways: it’s either a guy in a suit or it’s a puppet,” Dan says.

“In Hellboy, for example, Hellboy himself is Ron Perlman in a suit. So you’d take a cast from the actor and build a costume for him. And the guards in Hellboy, they’re guys in suits but with radio controlled faces, so they’ve got hugely expensive, very highly engineered robotics inside their heads.”

When the creatures don’t have people inside them, though, it’s a bigger job. “If you were building a kind of Alien-type creature, you’d build it full-size from clay,” Dan explains, “And then you’d make an articulated fiberglass skeleton, and cover it in foam latex.”

Do try this at home
Want to create some professional-standard effects for your Halloween costume this year? Dan recommends picking up a Sculpt Gel kit from Mouldlife.

“It’s a platinum silicone rubber that you mix together. It sets after about five minutes, and you can sculpt it into whatever shape you want – you could make wounds, or change the shape of someone’s nose or ears, or give them horns, or whatever you want.” he says.

Sculpt gel is affected by temperature, so keep it cold to slow down the setting process, or speed it up using a hair dryer.

The gel might stick to your tools or fingers, but Dan’s got a tip for that, too: “It doesn’t stick to potato starch, so use pieces of potato as tools to sculpt it into shape.”