See Notes about the instructions.
This is the easy and safe way to cast doll shoe soles. It may get a bit messy, but there are no hot liquids to deal with and the mess is easy to clean.
First you need a master of the sole. The easiest type to produce with this method is the wedge sole. You can make other types of soles by combining this method and the copper sheet and leather method. In that case, you need to cast two separate parts as shown in the second picture below.
Balsa is very good for carving the master. It is soft and easy to cut, but can be sanded to have a smooth surface. It needs to be varnished or painted when ready.
When you have the master, it needs to be attached onto a piece of cardboard or plastic sheet. You can use small amount of glue or tacky wax, for example.
Next you need to apply the latex on the master and around it on the cardboard. Follow the latex manufacturer's instructions on this. I use a brush to apply several (4-5) coats of latex. Allow the latex to dry before applying the next coat. You can see when it is dry as it turns to yellow.
When there are enough layers and the latex is dry, it is time to remove the mould from the master. First apply some talcum powder on the mould to keep its parts from sticking into each other. Stretch the mould as needed to get it off and turn it inside out. Apply talcum powder also to the inside to keep it from sticking and turn the mould back the right side out.
Leave the mould alone for a couple of days. When ready to do the casting, mix the plaster, set the mould so that the plaster surface will be level, and pour in the plaster. Leave it to dry.
When the plaster is dry, remove the casting from the mould and let dry for a day or two, maybe even longer, depending on the size of the casting. The casting is dry when it does not feel colder than the room temperature anymore.
You can paint the casting or use PVA glue to cover it with fabric, leather, etc. Make sure that the entire surface of the casting is covered somehow, so it will be less prone to dents in case it is handled carelessly.
Note: You should still have the master intact and you can create additional moulds, if you wish. If you make another identical mould, you can cast both soles of a pair at the same time. You can also attach some decorations to the master, create a different mould, and use that mould to create soles that have decorations, which you can paint to make them stand out.
See also the article on the Model Makers Resource.