Traditionally the ears would be sculpted in clay, a mould made and the ears cast using foamed liquid latex. This can be long winded, technically challenging and expensive due to the sculpting skills, additives and baking required. Also once the mould is made it can only produce that design of ear.
Here's my take on a slightly different approach, using two kinds of armature. One type will allow you to make any design of ear you like, but requires more work at the fabricating stage. The other requires more work on the armature but can then produce lots of sets of ears reasonably quickly.
All these ears rely on the slip latex or skin latex process. This requires no additives or baking at all.
The two images here show the small ears fitted but without make up added, and a pair of the long custom ears as part of a Dark Elf body painting.
Before you begin please be aware that these ears are made of natural latex. Some people are allergic to latex either in it's liquid or cured state. Most people over the age of 18 would be aware of any allergies, but to be sure do a very simple test on the back of the hand.
Using a small amount of liquid latex and a small sponge dab a thin layer about an inch or 25mm in diameter onto the back of your models hand. Allow a few minutes for this to cure (it will go transparent). Apply a second thin layer and allow that to cure as well. If after this time there has been no reaction then it is very unlikely that there will be problems. Gently roll an edge with your finger to lift it and peel off the test patch.
Some people with very sensitive skin (those who have difficulty finding suitable make-up for example) may show a very slight reddening and mild itching of the area. This is normally not an allergic reaction, but a reaction to the very small percentage of ammonia present in all liquid latex (usually less than 0.5%) used to prevent the latex from curing in the bottle. The ammonia will evaporate as the latex cures.
Step 1: The Basic Armature
Or you can make a very basic sculpt from Plasticine and make a mould from that then cast in plaster or resin.
To get a basic shape you can put a piece of tracing paper over someone's ear and simply draw the outline in felt tip pen. Try to find someone who has average sized ears when you do this.
Since these false ears fit only to the top and back part of the outer ear, we are only really interested in the Helix and Lobe. The rest of the ear does not need any sort of moulding or shaping for a generic ear.
In order to make both types of ears in this 'ible you are going to need two pairs of armatures. Two left and two right ears.
If you want ears for a specific person, and want them to fit exactly you can cast their real ears. Do a search of the net for making an alginate casting of an ear, which is beyond the scope of this particular 'ible.
Finally, if like me you are lucky enough to find a department store with a broken shop dummy they will give you, some of the fibreglass ones have reasonable ears that can be moulded with liquid latex and then cast in plaster or resin.
You need to have a nice rounded edge to the helix and lobe, so use sandpaper or a Dremel / Rotary tool if yours aren't smooth enough. Also sand the backs if required. You need the armatures to be between 1/4" (6mm) and 3/8" (8mm) thick. This is about the thickness of an average persons helix and lobe.
Step 2: The Small Ear Armature
For my armatures I took two basic plaster ones and used Milliput (a two part epoxy putty) to add the sculpt.
The sculpt is very simple to do so don't be put off. Knead and work the putty until it is malleable, then make a small triangle of putty the same thickness as the helix of your armature and place it in position on your basic armature. The putty is workable for quite a long time so you can pull it off and start again if you are not happy with it. Try and blend the joins smooth.
Once you are happy with the triangle section, roll out a long 'sausage' of putty a little thicker than the triangle and stick it on running from the bottom of the lobe up and around the triangle to the top front of the helix. Again try and smooth down the edges.
Let it all cure fully and you should have two nice pointy ear armatures.
Step 3: Making the Small Ears
It takes about an hour for each coat to cure before the next one can be added. This process speeds up in warm weather or under a small heater if you are in a big rush. I normally do a coat, go and do something else for an hour, come back and do another coat and so on. You need to cover down as far as the helix and lobe at the front, but only a much smaller section at the rear. Down to overlap the basic part of the armature by about 1/8" (3mm). The main area for gluing onto the real ear is at the front.
Once all 6 layers are fully cured, give the entire thing a generous brush over with talcum powder to prevent the latex from sticking to anything else (including itself).
Gently start to lift one edge of the latex. As soon as it starts to lift brush some talc under it. Continue to peel and powder until the entire ear has been peeled off. The powder is important because if untreated latex touches untreated latex it will bond to itself instantly and the ear will be ruined. Use plenty of powder, it won't matter at all.
You should end up with two hollow latex ears.
Step 4: Making custom ears
You need to find a soft dense foam the same thickness as the helix of your armature. I have found that those really cheap 6mm thick camping bed roll mats are ideal. They are made of a soft version of EVA foam and are abundant in the shops during the summer camping season. They are actually pretty useless as camping bed rolls since they tear and 'bruise' very easily and are probably only intended for use on a single trip. They are very cheap, I have seen them in 'pound shops' and in larger supermarkets for less than £5.00 GBP. You would easily get 100 pairs of ears out of one roll.
The method is very simple. Lay out your foam and draw the outline of your armature onto it using a felt tip pen. Now design the size and shape you want your ear to be. Cut it out using a VERY sharp scalpel or craft knife (X-Acto or similar). Flip it over back onto your foam and draw around the first one using your felt tip pen. Cut out the second one. You now have a matching set of ear extensions.
The next part can be tricky. You need to hollow out a mild curve in your foam where it is to join the armature. I use a Dremel fitted with a small drum sander, but it is possible to use some fine grit sand paper and do it by hand. The Dremel does it in seconds.
Next you need to 'sculpt' a simple ridge round the shape of you ear about 6mm (1/4") inside the edge to simulate the helix of the new ear. This does not need to be anything fancy at all, just a simple indentation of a couple of millimetres (1/16") deep will do it.
Now take your latex and paint a layer into the mild curve at the base of your foam, along with a matching layer on your armature and allow it to dry for half an hour or so. Do this on both the foam parts and both the armatures. Once cured carefully position the foam part onto the armature and gentle press it on. it will bond instantly.
From this point on simply follow the instructions we used for the small ears. You need 4 to 6 coats of latex over the entire foam part and down over the armature to the same distance as shown for the small ears. Once all the layers have fully cured give a good dusting over the outside with talc and gain use plenty of talc under the latex as you peel them off.
Step 5: Fitting the ears
First offer up the ear to your model without any adhesive and check the fit. You can trim the edges of the latex ears with a small pair of very sharp scissors to obtain the best looking fit. Ensure that there is enough latex on the edge of the ear to cover the helix at the top and down the length of the ear.
Using a cut up bath sponge with a little liquid latex on it gently coat the bevel at the base of the elf ear with a very thin layer of latex. ensure that the adhesive goes right to the edges. Do the same on a matching section of your models ear. Be careful not to get the latex in their hair. You will have a devil of a time getting it out!
Leave the adhesive on both the elf ear and the real ear to go transparent. Next carefully position the elf ear onto the real ear, it will bond instantly. Gently smooth down the edges so that they blend into the real ear as well as possible.
Next use a Q-Tip dipped in latex and run a small 'fillet' of adhesive over the joint between the real ear and the elf ear. Let it go transparent, then use a blusher brush to talc the joint areas. You can then use some skin coloured foundation to colour the elf ears and blend out the joint. The ears will also accept face or body paints if you are doing a character piece.