...Mould it and make it out of rubber with a multi part mould

This How-to will tell you how to mould a more complicated piece and make the finished item in rubber. This technique is used for complex shapes which would otherwise be impossible to remove from a one piece mould.

Make sure you read the How-to on making a simple rubber piece before you attempt this.

As with the single sided example the original item has been sculpted from Oil Based Clay which is non-air drying. This is important so it remains pliable and we can easily remove the piece from the mould. In this example, two blank eyeball forms have been fitted which will be replaced with painted eyes in the finished piece. These eyeball forms will help retain the right shaped eyeball socket in the piece throughout the moulding and casting process.

Important: Oil Based Clay is reusable - you can use it time and time again to make different sculpts once you've finished with the moulding stage of the process.

Unlike the single sided example, this piece has a front and a back that we will need to mould. To do this we will need to make a two part mould in order that we can get all the clay out of the plaster.

The sculpt is divided into two with water based clay. This clay will not stick to the oil based clay, and it will also separate from the plaster provided it is not left to dry out. The idea is to get the water based clay to meet the oil based clay as close to a right-angle as you can - this will enable easier removal of the water based clay. Also the join from water based clay to oil based clay should be as tight and clean as possible.

At this stage, you may wish to seal the water based clay with a petroleum jelly (like Vaseline). This help you remove it from the plaster after the first mould half is done, but is generally optional - if you remove the clay at the right time it won't stick. You may wish to experiment with some clay of both types and some plaster before trying it for real on your sculpt - you only get one chance to make the mould as the process of removing it from the clay will destroy the original.

In the example below some dips in the water based clay wall have also been made which will make it easier to fit the two halves of the mould back together later:

As before the front of the sculpt is covered with multiple coats of plaster, and in this case it has also been reinforced with modroc plaster of Paris bandages:

Once the plaster has set you can remove the water based clay. Important: make sure you remove the water based clay while it is still wet, do not allow it to dry out. Peel it away slowly and try to get it all off in one piece. Make sure all the Water based clay is gone - you may have to carefully remove any that is left, being sure not to mark the original oil based clay sculpt.

Once that's done you should have half the original clay sculpt stuck in plaster and the other half still exposed. The next step is very important - you MUST cover the plaster face with something to prevent more plaster from bonding to it. In this example a petroleum jelly (like vaseline) was used: A water based clay base has also been added to the piece and it has been laid flat to make the application of the plaster to the back of the piece easier:

As with the front, several layers of plaster have been built up, followed by a layer of modroc plaster of Paris bandages for reinforcement:

Once the plaster has set, the clay base can be removed. Dig out the middle of the clay enough to be able to grip both sides of the mould:

Gently pull the two halves apart - provided you applied the petroleum jelly or something similar correctly they should easily separate. Note that the dips we made in the water based clay wall are now present on both sides of the mould and fit perfectly into each other making mould reassembly much easier:

Clean any excess clay and petroleum jelly from the mould and test reassembly. In this example the eyeball forms have been glued back into place as replacement eyes will be fitted later so we need to leave space for them in the final piece. You could just as easily leave them out and make the eyeballs as part of the main latex piece.

You can see the seam between the two mould halves in the example, making this as fine as possible comes with practise - it's mainly down to the quality of your water based clay wall. However, in this example you'll be able to see what the effect of a less clean seam is - effectively it just means the finished piece will have to be trimmed later on:

Next it's time to apply the latex to the mould. This time green pigment has been used - as you may have guessed the item is intended to be some sort of alien. Pigment is added to latex at around 5% - as with the single sided example it will dry much darker.

Layers of latex are built up in the mould by partially filling it and tilting it around, and also by brushing latex over the edges and onto any parts that get missed:

Once five or more layers are complete and dry, it is time to remove the piece from the mould. As you can see the piece looks fairly tatty - the seam between the two plaster mould halves has had latex seep into it as well as partially around the front eyeball. We have left the back eyeball out for now so the socket can be seen:

After a trim with a sharp pair of scissors, and a wash with water to get the bits of plaster out, things looks much better. The mould seem line is still partially visible, but this is the often the case even with commercial products - with practise at the water based clay dividing wall stage this can be reduced even further: