Deep sea diver.
Alien chestburster.
Together.

Right...

At first glance, that might seem like an odd combination of costume themes, but I promise you there was a logical thought process behind it.

This Halloween I wanted to make a high-quality Alien chestburster prop that could erupt forth unexpectedly at parties, evoking horror and hilarity before laying down some bustin' xenomorphic boogie on the dance floor. Obviously this would require a glove puppet of sorts, plus a costume that could conceal the fact that I had one arm hidden inside my clothes for much of the time.

My solution was to make a prosthetic arm which could spend the evening holding some other prop so that nobody became suspicious of its inactivity. A spacesuit seemed the natural choice of clothing for an Alien victim: it would fit the theme, provide lots of bulk to conceal the puppet and give me a convenient prop (i.e. the helmet) to hold under my fake arm.

Then I was invited to steampunk Halloween party. Yes, I know.

I decided that rather than try to build a fully functioning neo-Victorian spacesuit, I'd go with a more recognisable deep sea diver outfit, built to a similar template. If pushed for an explanation, I could claim either that it was a prototype suit for very early spacefaring pioneers or that I had been impregnated by an Alien facehugger while exploring the ocean floor. Either way, I had an entirely plausible backstory. Such things are important.

If you want to make this costume yourself you can, of course, adapt it easily into a more modern spacesuit or use the alien puppet with a different costume entirely. Even on its own, the puppet is a lot of fun for scaring people.

Now that I've justified the costume's existence, let's talk about how to build it. I'll divide these instructions into five sections:

1) The alien puppet.
2) The helmet and collar.
3) The prosthetic arm.
4) Other bits and pieces.
5) Putting it all together.

Let's get going!

Please note: This Instructable will take you several days to complete, due to drying times for paint, glue and latex at various stages of the process. If you're planning on wearing it for a specific event, I'd suggest you start work on it at least a week beforehand.

Step 1: 1) the Alien

The Alien* puppet is definitely the most time-consuming part of this project and, in my opinion, a worthwhile standalone project in its own right. For that reason, I've made it into a separate Instructable which is viewable by clicking here.

Please follow the link to read full instructions for sculpting a character out of plasticine, making a plaster negative and then casting a puppet out of latex. If you're already comfortable with how to do all that, then carry on reading and I'll summarise the process.

-- Start by making your Alien from plasticine. Try to size it so that it will fit nicely over your hand and forearm. Make it as scary-looking as possible.

-- Use the clay model to construct a two-part plaster negative mould, along with separate moulds for the Alien's arms and the roof and floor of its mouth.

-- Pour latex into the plaster moulds and leave it to dry. Assemble the different pieces around your own hand, using superglue to stick them together. Be careful not to stick the Alien to yourself.

-- Paint your puppet.

I know that looks like an easy process when I write it out like that, but please believe me when I say that it takes a long time. Labour time aside, the latex still takes several days to dry, which is why this won't work so well as a last-minute costume.

*Capital A in Alien to show a bit of respect for the Alien film franchise. I say "film" rather than "movie" because I'm British. This also explains my bizarre spelling habits and colloquialisms. I'm dreadfully sorry. Blimey.

Step 2: 2) the Helmet and Collar

Crikey, that Alien took a long time to make. Let's press on with the rest of the costume.

To make your diving helmet, you'll need the following bits and pieces:

- Two large plastic mixing bowls*.
- An assortment of plastic flower pots and drainage dishes.
- A plastic yoghurt pot.
- A piece of paper with a straight edge.
- Thick, stiff card.
- About 1.5 metres of plastic aquarium tubing.

For the collar, you'll need:

- Some flexible foam scraps.
- A covering material that can be painted, e.g. artificial leather.

You'll also need:

- Spraypaints in the following colours: Black, bronze, copper.
- A marker pen.
- Plenty of glue. You will probably need superglue as well as ordinary craft glue.
- A sharp craft knife.
- Scissors.
- A file.
- Masking tape.

*Put rim-to-rim, these bowls should make a rough sphere large enough to comfortably fit your head. One of the most entertaining parts of this Instructable was going to the kitchenware department of a large shop and trying on different bowls while trying to avoid the judgemental glares of the sales assistants.

Step 3: Prepare the Portholes

Lay out your bowls and flower pots so that you can see how your helmet will eventually be formed.

The two bowls will make the main sphere of the helmet, while the flower pots and drainage dishes will provide the portholes. With a little bit of imagination, it's starting to look like a helmet before you've even begun... Failing that, skip forward a few steps to see how it will look once it's finished.

At least two of the portholes will be lying over the seam where the two bowls' rims meet. In order for the portholes to lie flush against the surface of the bowls, you may have to cut small slots in the rims of the pots/dishes.

If you need to trim one of your flower pots down significantly, as I did, you'll need to do so in an even fashion. Take a piece of scrap paper with a straight edge and form it into cylinder, then tape it around the pot. Use this as a guide to mark where you will have to trim the pot, then cut it to size with scissors.

There, isn't that looking more like a helmet?

Step 4: Still Fiddling With Portholes

Use scissors to cut holes in your drainage dishes as required.

Use circles of thick card to fill in any missing bits of porthole, then file away any rough edges.

Cut short segments of plastic aquarium tubing and glue them into your portholes to provide bars.

Step 5: Make the Helmet Rim

You're going to need some way to get your head in and out of this helmet, so let's make a head-hole with a rim.

Bend several thin strips of card into a hoop just big enough to fit your head through, then glue them together.

Place the hoop on the base of the bowl which will form the lower half of your helmet. Draw around the hoop'sinside with a marker pen and cut away where you have marked. Do this slowly, as plastic bowls are often prone to shattering.

While you're in a slicey mood, cut away holes in the bowl for the portholes as well.

When you're sure you don't need to do any more cutting, glue the two large plastic bowls together. Once the glue has dried, glue on the rim you made earlier.

Now would also be a good time to trim your yoghurt pot into a short cylinder and glue it to the helmet. Add a circular card base to the yoghurt pot to cover up any unsightly recycling symbols that might show through the paint.

Don't glue the portholes to the rest of the helmet yet, as you're going to paint them separately. You should now have something that, if worn on your head, makes you resemble a watercooler. Hey, there's an idea for next year's costume...

In the picture below, I'm also wearing the diving suit collar. We'll talk about how to make that in the next step.

Step 6: Construct a Collar

Obviously you can't just stick a plastic bowl over your head and expect to survive in the perilous depths of the ocean. To make a convincing deep sea diving suit, you're going to need a collar.

The basic collar is made out of four pieces of recycled foam, originally from packing material and camping mats.

Cut one piece into an ellipse, then remove a small section of it. This way, when you join the cut ends together, the piece will become slightly conical rather than completely flat. It's a small detail, but it makes for a better shape.

By trial and error, trim a second piece of (thicker) foam so that it makes the vertical section of the collar. You should end up with something that looks like a neck brace.

Use long, thin scraps of foam to make the rim of the collar. Hold all of this together with tape or pins for now, then try it on to make sure it fits.

If you don't have a mannequin to help you, it's handy to have a cushion or a pillow to support the collar while you're working on it.

Step 7: Cover the Collar

Disassemble the collar and use the pieces as templates for the artificial leather covering.

Be sure to cut out pieces of fabric a few inches larger than the original foam pieces.

Now reassemble the collar with its new covering, this time gluing it together as you go. Start by gluing fabric to the foam ellipse and trimming it to size.

Glue the foam collar on top of this, then wrap it in another piece of fabric. To tidy up the top of the collar, cut a series of flaps into the fabric and fold them over to the inside of the collar. Then line the inside of the collar with another long strip of fabric.

Glue the foam rim in place and glue dozens of small strips of fabric to it, as shown below. Once these have been glued down, you can fold them over to cover the lower border of the collar in the same way you covered the upper border.

Step 8: Paint the Helmet and Collar

Now that you've assembled your helmet, portholes and collar, you can paint them.

Start with an undercoat of matte black spraypaint for everything, then paint on the bronze details. Also paint the portholes entirely bronze.

Once this has dried, mask off the bronze areas with tape and spraypaint the rest of the helmet and collar copper.

If it all looks slightly too new and shiny, spray a light mist of black spray over it to give it a duller, more worn look.

Step 9: Glue the Portholes On

Use superglue to attach the painted portholes to your helmet.

Stand back and admire your handiwork.

Step 10: 3) Make the Prosthetic Arm

To make a fake arm, you're going to make a quick and dirty cast of your own arm.

For this, you will need:
- Cling film.
- Parcel tape.
- Garden wire.
- Card.
- Scissors.

Start by holding your shiny new helmet under one arm. Try to find a comfortable, natural-looking position that doesn't leave the helmet in front of your chest. Remember, that's where your Alien is going to emerge!

Now, keeping that arm in its position, use your other hand to put the helmet aside and wrap your stationary arm in cling film. Once it's covered in cling film, cover it in several layers of parcel tape. Don't wrap it too tightly, or you will lose circulation. And possibly fingers.

After a few layers of tape, you should feel that the wrapping around your arm is becoming stiff enough to hold its own shape. At this stage, carefully cut a slit down the side so that you can remove your real arm.

Reinforce the inside of your prosthetic arm with card and tape over the seam.

Take a length of stiff garden wire and bend it into a loop. Squash the loop so that it will fit down the inside of the prosthetic arm. This can now form a posable frame for the prosthetic arm.

Fashion the rest of the loop into a shoulder harness, as shown in the images below. Tape a few scraps of foam onto the wire for comfort.

Step 11: 4) Other Bits and Pieces

To complete the costume, you'll need the following bits and pieces:

- A boiler suit.
- Gloves.
- A weight belt.
- Weights for your shoes.
- Fake blood (optional)

For the boiler suit, choose one which is a neutral beige, brown or orange. Make sure it is very baggy and has a convenient opening down the front so that your Alien can pop out. I managed to find a jacket with popper fastenings (i.e. snap fasteners or press studs) down its front and a matching pair of trousers. That is to say, the trousers matched in colour. They didn't come off suddenly using popper fastenings. It wasn't that sort of a party.

Almost any gloves will do, as long as they're not of a very inappropriate colour. Lurid pink gloves might detract from the authenticity of the rest of the suit.

To make a weight belt, cut several pieces of foam into roughly rectangular blocks and whittle away the corners so that they resemble large smooth pebbles. Then spraypaint them in black and grey and tie them onto a canvas belt with scraps of leather or brown parcel string.

To make weights for your shoes, cut some angular shapes out of card and spraypaint them silver and black. Then just attach them to the surface of your shoes with double-sided tape.

There are many recipes for fake blood available on this site and elsewhere on the internet, so I won't go into how to make it here. I chose not to use any for my costume, as I wanted to preserve my jacket for another costume. Opting not to have fake blood all over me also meant that I didn't make a mess of other people's costumes and that my Alien was always a surprise when it popped out.

Step 12: 5) Putting It All Together

Most of this costume's final assembly is self-explanatory, but sorting out the fake-arm-and-helmet combination is rather fiddly. If you just try to attach the helmet directly to the arm, it will tend to fall off repeatedly.

Instead, you're going to attach the helmet to your shoulder by a loop of string. This way, even though you will appear to be holding the helmet under your (fake) arm, it will in fact be dangling from your armpit. The false arm will serve to stop the helmet from swinging around too much, but it won't be taking any of the weight.

Make a pair of holes in the top of your helmet, as shown below. Also, make a small hole somewhere discreet on your jacket or boiler suit, either in the armpit or on a chest pocket if it has any.

When you come to put your costume on, start by donning your prosthetic arm. Then put your jacket on, putting your false arm through the jacket sleeve and leaving your real arm inside the jacket. Then feed a length of string through the holes in the helmet, into the hole in your jacket, over your shoulder and back out of the hole in the jacket. Tie it in a loop so that it takes the weight of the helmet and holds it snugly up against your underarm.

Dress your prosthetic arm in a glove and adjust it so that it is holding the helmet in a convincing position, then fold the fingers up into the inside of the helmet and attach them there either with tape or with another piece of string.

Your helmet should now be supported from above by a loop of string and, less firmly, from below by your prosthetic arm.

Now you can put on your weight belt and shoe weight.

Before you insert yourself into your Alien, I recommend powdering its innards with baby powder or talcum powder, as your hand will get quite hot and sticky otherwise. Put the Alien puppet onto your hidden hand and conceal it well underneath your jacket.