Making A Vintage Diving Helmet

Back in November I had a post about "The Last Expedition", an incredibly detailed mythos LARP run by The Dark Door group in London. The whole adventure was filled with impressive props, but the one that really stood out was the full-scale vintage diving suit built from scratch. What follows is the build log of the suit's helmet written by Richard Bird, the man behind it's construction.

My sincere thanks to Mr. Bird for taking the time to write up his experience as well as his generosity in sharing it.



First of all, thanks to those people who expressed in interest in how this was made. It was built to be as realistic as possible while being LRP safe (i.e. the person inside was not going to suffocate!) As I’ve been aching to try out cold cast metal for a while I thought this would be a good opportunity to give it a go. The only problem was I’ve only ever seen small bits made out of cold cast metal so I was unsure if it could be done! However, hopefully I proved it can be.

Step 1: Size

The first problem was size. I know what a diving helmet looks like but getting the actual size proved to be a bit of a bind. In the end I settled on best guess looking at photos. Looking at the finished product I would say the helmet part is a bit too big but it was good enough for our needs.

Step 2: Template

I made a cardboard template for the breast piece just so I could get some idea of size, shape and angle of the curve over the shoulders to allow someone to get their body in to wear it. Plus it gave me a chance to work out the size of the hole for a head!

Step 3: Breast plate

The breast plate was shaped out of MDF and filler to match the cardboard template. The curve of the breast plate over the shoulder was achieved by small strips of MDF stuck to masking tape then flexed into the required curve which was then smeared with PVA glue. Filler was used in the gapes when it was dry then sanded.

The raised edges of the breast plate were created as above however I made it separate purely so it I could smooth the inside edges of the curves without touching the breast plate to give it a nice ‘right angle’ fit against the plate.

The ‘neck’ was tricky because I wanted it to be perfectly round. I couldn’t find a big enough a piece of plastic pipe for this so I built it from ring after ring of cardboard glued to one another. Once that was dry the cardboard pipe was smeared in resin, which allowed it to be sanded afterwards. Again, filler was use to smooth off and smooth the join when attached to the breast plate. An slight ornamental design was added to the bottom of the breast plate just to give it something interesting to look at, which was simply cut out of a bit plastic card. This also handily covered up the join between the two sections of the raised edges.

A final layer of filler was added over the wood to give a smooth surface and a layer of gloss paint sprayed over it to hide any small pits.



Step 4: Helmet:

Now this was tricky. I looked everywhere for a ball big enough for the helmet which I could cut up without losing its shape. In the end I ordered a 450mm polystyrene ball from ebay which came in two halves. The initial plan was to glue the two halves together then fill the gap and paint it numerous times to lose the patterning of the polystyrene. However that did not give the result I wanted so in the end I smoothed off the entire ball with (a lot of) body filler and a mouse sander which did the job like a dream. Please note if you do the same then be aware body filler melts polystyrene so you end up with a filler ball that can be very thin and fragile.

Once that was done the holes were cut out for the portholes, the neck and the proposed ‘valves’.



Step 5: Fixtures

The portholes where created in the same way as the neck with circles of cardboard finished with plastic card. I built these on the helmet so I could match the curve of the surface and ensure a smooth fit but I placed cling film down so the porthole wouldn’t stick. The bars were copper brazing rods but these would be placed in the mould when casting. Note: I only made one of the side portals as it was cast twice and flipped over for the other side portal.

The valve base and the top breather where simply caps to spray cans with some plastic dressing added to them. The Valve came from a plumber’s merchant.

Step 6: Moulding

One piece moulds were taken of the portholes, fixtures and fittings using silicone rubber – while I could have used latex as only one casting required (resin and latex don’t work that well together over time) I needed something which would cure quickly so I wouldn’t be delayed for long. For the breast plate and helmet I used latex braced with cloth and backed with a fibreglass support – this was done to keep costs down. The breast plate was done as a one piece mould. The helmet mould was planned to be made as a one piece as I was keen to do everything I could to keep its sphere shape, however the latex mould proved to be too floppy even with fibreglass support and would simply fold in on itself once when you tried to cast, so eventually this was done as a two piece mould.



Step 7: Cold Cast Metal

The key to using cold cast metal is to make sure you use enough metal. Sounds obvious but it’s easy to scimp on the metal to make the mixture pourable but it does you no favours. I found the best mixture was to use Polyester General Purpose Resin (not clear resin) with a ratio of 1 part resin to 3 part metal (325 mesh). When mixing put the resin in first and gently mix the powder in after afterwards a small bit at a time. You want to get it as a runny paste (like wallpaper paste). When putting it into the mould make sure you take your time and ensure all the air bubbles are gone as it’s going to be near impossible to fill afterwards without ruining the finish of the model. I normally run a finger (while wearing gloves) inside the mould to push the mixture into every part and push out any air bubbles.

As it’s thick you can coat all the sides of the mould with the mixture then fill the inside of the casting afterwards with a cheap filler. With portholes, breast plate and helmet i used a thin layer of the resin + brass, put a couple of layers of fibreglass in then filled the remainder of the casting with resin + iron which gave a lovely weighty feel to everything plus good strength.

Step 8: Finishing

Once everything was solid they were taken out of the moulds and cleaned with metal polish. I have read about using wet/dry paper however I found this dulls the metal too much and make it much harder to shine. Then everything was stuck together with epoxy glue. The front and rear valve had holes in to allow people to breath once inside the unit. Plexiglas was used on the portholes.

Two rings the size of the breast plate’s neck hole connected the helmet to the breast plate. One ring had the bolts in and was glued and screwed to the neck piece. The other ring was glued and screwed to the helmet and had holes to go over the screws so it would be bolted into place. The ring was cut out of a piece of MDF, moulded and cast in the same way as above, though if I did them again I would make them thicker to add more strength.



The finished item not only looked realistic but also feel realistic with a number of people thinking the diving helmet was made out metal. The brass feels cold to the touch even tarnishes over time so I can recommend this method if you need a prop to look and feel made of metal.

Richard Bird

The Dark Door