...Mould it and cast it in something solid with a multi part mould

This How-to will tell you how to make a flexible mould with a rigid support jacket for a more complicated piece,  and then cast it in something solid so it turns out the same as the original sculpt. This technique is used for items with two or more sides to them which would otherwise be impossible to remove from a one piece mould.

Be sure to read the How-to on single sided moulds before attempting this.

This item is a helmet for a full size wearable costume. The item is sculpted in an non-air drying, sulphur-free oil based clay. This clay is 'chemical free' so it will not affect the moulding substance and cause any issues. The helmet has been sculpted over a mannequin head and some cardboard so that it is not solid clay, which would otherwise be costly and heavy.

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.

In the same way as the single sided example, layers of latex and cloth were built up all over the clay until the desired thickness was achieved. Some latex 'lumps' made were made by layering up latex inside milk bottle tops which have been stuck on in various places - these are to make a 'key' for the mould to fit inside the rigid support jacket which is made in the next stage:

If we were to cover the item in plaster bandages as with the single sided example, then of course the item would be stuck inside and we wouldn't be able to remove it. Therefore we must make a two part support jacket.

This is achieved by making a clay barrier on the outside of the latex once it has dried. This barrier should divide the piece in half. Half the rigid support jacket is then made from Modroc plaster of Paris bandages:

After this, the clay barrier can be removed and the other half of the support jacket applied. The exposed edge of the plaster jacket should be covered with something to prevent the other half sticking to it - paper masking tape works well for this, alternatively a petroleum jelly can also be applied to the edge - but be careful not to get too much on the latex.

Here's the whole thing completely covered with Modroc, once it's dry (allow 1-2 days for it to completely dry) it can be removed:

The latex and cloth mould can now be removed from the clay, and everything reassembled leaving the middle hollow. You'll notice that the latex mould it really quite flexible which is why the support jacket is important:

Now the piece can be cast inside the mould, and of course multiple pieces can be made from it:

The next piece is the torso of the costume, and so it has a front and a back to it. As with the helmet it has also been sculpted over a mannequin form in order to save clay.

In the same way as the single sided example, layers of latex and cloth were built up over the clay. However, the front and back of the mould were first divided under the arms and over the shoulders. This was done by sticking playing cards into the clay in the appropriate places. The plaster bandage support jacket was also divided along these lines so when the mould was removed it easily came into two pieces:

This allows the two haves to be laminated separately which is essential in order that a person can get inside them when the costume is worn. Here are the raw casts made from Jesmonite and glass fibre fabric:

After the pieces are sanded and filled to remove any imperfections as required, they are primed and painted.

Warning: Always wear a suitable face mask when sanding items reinforced with glass fibre.

The costume can then be assembled, in this case a flexible board called Maplex Board was used along with some foam rubber and press studs to make four tabs to attach the back and front together:

For the legs of the costume a multi-part mould was also used, but this time we wanted to keep the item in once piece instead of having the finished piece split in two. Again the original piece was sculpted in Oil Based Clay, this time over wood and cardboard:

The sculpt is divided with playing cards, since this is the leg of the costume it is split at the knee, and also split partially length-ways in order that the mould can more easily be removed from the sculpt. In this case the support jacket is made from Jesmonite and glass fibre fabric as this is much stronger that Modroc:

The support jacket splits into a total of four parts for the whole leg. Each latex and cloth mould is left with a split in it along the same line as the support jacket split:

The finished pieces are cast from the inside of the mould in Jesmonite and glass fibre fabric, sanded & filled as required, then primed and painted: