Hi there, my names Sarah and I have created a "Two faced Harvey" character from the Batman series
Please take a look at my step by step process and have a go yourself :)

Step 1:

Firstly take a shirt and burn the neck on the left hand side using a lighter or any means ( I used a cooker but be careful)
Then burn the left side of a suit jacket using the same method as the shirt, remember to burn the back as well to match.
Find a suitably coloured tie (mines from primark)

Step 2:

To create my make up process I have made two prosthetic pieces

To do this I took a wooden board and some plasterleine (sculpting clay) and sculpted a Harveys mouth shape out using metal modeling tools to create the burnt away skin effect to show the teeth,
I ensured that the part to be stuck on the lip would be separated to aid application and to create a realistic edge.
The surrounding edges need to be smooth so when applied the edges blend in with the skin and don't look fake and stuck on.

One i had done this I sculpted an eye shape similar to Harveys in the film in the same way. Always refer to a reference image when sculpting to get your desired look.

Once completed take some plastercine and build a wall around your sculpt making sure you leave a two cm gap from the sculpt to the wall. make sure there are no gaps in the wall as you need this to be water tight. if you are unsure fill with water to block up any leaks. make the wall high enough so when filled the mold making rubber will cover the sculpt fully.

When you are happy with your wall mix your mold making rubber up (you can buy this from on line or an arts and craft store such as hobby craft) (follow instructions on the packet for mixing as every brand is different) pour the mixture in to the wall and completely cover the sculpts.

You can see in the picture I have also sculpted other cuts in my wall for other uses not for this make up application

The rubber will usually set over night
once dry you can then pull the rubber off the board and you will be left with an impression of your sculpt, clean out any clay that has been left in the impression and your ready for the next step.

take some latex and pour this into your clean mold and leave to set over night

Step 3:

When your latex has dried powder over with talk and remove from the mold
you will then be left with your prosthetic piece
you can now color this using creme make up/ powder eye shadows or face paint see what works bet for you

Step 4:

Take your model and apply a bald cap (you can either make your own or buy one)
To apply the cap put spirit gum around the edge a the front stick to the skin , then work your way around the back ( remember to patch test all materials prior to use for any allergies)

once the bald cap is secure an dry apply the prosthetic's to the face using spirit gum
take toilet roll and rip into pieces using latex apply the tissue all over left side of the bald cap down the back of the neck and over the left side of the face where needed

Once dry you can then cut away the right side of the bald cap so the hair can be exposed leaving one half bald. Then color the tissue using whatever make up you like
I have used eye shadows and creme makeup

Add the costume and your finished :)