They are also often used as the basis for other make up SFX effects and for headpieces, or to cover up the hair when making face and head life casts.
Bald caps are easy to make, and the materials aren't too difficult to assemble. You will need:
A polystyrene, glass or fibreglass head (used for hat displays and similar).
Some cheap bath sponges
DVD marker pens
PVA Glue (if using a polystyrene head).
Without doubt the most important, and possibly most difficult to acquire is the head. Glass ones are the best but they are expensive. Mannequin fibreglass ones can sometimes be found at car boot sales or bankrupt stock, but you can use a polystyrene one perfectly well. These are cheap and readily available on the net. I got my mannequin head for nothing from a closing down sale, and the polystyrene one cost me a fiver with postage.
Step 1: Preparing Your Head
If you can only get a polystyrene head then you should consider preparing it for use. You can make bald caps using the head as is, but eventually the soft surface of the head will start to break down and lumps will get pulled out of it.
You need to give it A LOT of coats of PVA glue to seal and strengthen it. I took 3 weeks and 25 thin coats of PVA, allowing each one to dry in between. This gives a really tough and non-porous 'skin' to the head so I can use it for all sorts of work. Obviously it won't take heat or serious chemicals which will both melt it.
Once you have a sealed head it is advisable to mark it. This will allow for good feathered edges to your bald cap. Decide if you want an all over cap (which must be cut back), or if you are happy that the ears can be left out.
Mark the head using the DVD pens (I use different colours for each edge) such that the first line covers the entire area of the cap, the second is about 1/4" (six millimetres) inside the first, the third is 1/4" inside that and the fourth 1/4" inside that. See the picture for a visual guide.
Your head is now ready.
Step 2: Adding the Rubber
I'm using blue latex here so you can see what's going on. the latex can be brushed on if preferred, but I find that the stippling effect of the sponges leaves the final surface of the bald cap with a very realistic 'skin' texture.
Keep reloading the sponge as required. Your are looking for a thin even coat.
If the latex begins to dry out you will see it lifting the latex you have already laid down, keep the latex on the sponge wet to avoid this happening. Once the entire area of the cap has a thin even coat, leave it to dry for a couple of hours. You can try to wash the sponge out under running water, but I don't bother, I just discard the cube and use a new one for each coat.
Once the first coat has dried, start on the second coat but only bring this one out to your second line. Again, keep the sponge wet to avoid lifting the lower layer. Work evenly and thinly over the cap. Let this layer dry. Then repeat until you have four layers. Allow the whole thing to dry overnight.
Step 3: Dicision Time
If the cap is needed as a thin under layer for make up alone, or to make someone look bald, then add another couple of thin layers to the innermost line and leave it to dry.
If the cap is for sealing the hair for life casting add another 4 layers to prevent the possibility of tearing and allowing the casting medium through.
If the cap is to form the basis of a prosthetic head piece then add at least 6 more layers for strength, more if required.
Allow the entire thing to dry thoroughly. The latex is usable after 4 or 5 hours but really needs a couple of days to cure completely. Natural latex will take on a straw colour once it's fully cured.
Step 4: Removing the Cap
Then find the outermost edge of your outermost line somewhere at the back of the cap. Using your fingertip, GENTLY roll the edge until it just starts to lift. Get the blusher brush covered in talc and force some powder under the edge. Lift it a little and brush it again. Once you can get a decent grip on this lower edge, start to peel the cap away from the head forcing talc under the rubber as you go. If raw latex touches raw latex it will instantly stick to itself, unless it has some talc on it.
You can go overboard on the talc, it won't matter if there's powder everywhere as long as the cap doesn't stick to itself. Eventually you will have the whole cap off, and you will be amazed at how tough the thin rubber really is.
Step 5: Fitting the Cap
Have a look
For a video of a bald cap being fitted by Peter Gaal.
Cut it using small sharp scissors being careful not to decapitate your victim (er.. model), or slicing off their ears or poking them in the eye etc.
The edges can now be stuck down using liquid latex, spirit gum, pros-aide or similar theatrical glue. Run a fillet of latex on a q-tip round the edges to feather them out.
You can now cast your model, or add make up or whatever.
If you are building a prosthetic, it is best to do this while the bald cap is still in place on your mannequin.