...Mould it and make it out of rubber

This How-to will tell you how to mould a simple piece and make the finished item in rubber.

Firstly you must sculpt the item that you wish to produce, for this example Oil Based Clay has been used. Oil Based Clay is a non-air drying clay which is important so it remains pliable throughout the process. The item has been built up by hand on a piece of plastic - the lid from a plastic tub in this case.

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.

A clay barrier has built up around the edge of the piece. This step is not always required, but in this case it will make the job easier and save a lot of mess.

Next you will need to mix up a hard casting plaster such as Herculite-2 or Crystacal-R to make a negative impression from the clay piece. This will involve pouring plaster over the item until it is covered with a thick layer. As the plaster is very runny to start with it may be necessary to spoon the excess back onto the top to make sure that it is evenly coated - this is where the clay barrier around the outside of the working area is important.

This may require several lots of plaster to be mixed up in order to make a good thick plaster piece. You may also consider reinforcing the plaster with a scrim fabric or Modroc plaster of Paris bandages to add extra strength depending on the size of the piece:

Once it's all set up (allow at least 24 hours for it to dry through), you can remove the clay barrier and remove the plaster from the plastic base. Now it's time to remove the clay which is why it's important to use a non-air drying clay such as Oil Based Clay. Carefully separate the clay from the plaster and make sure all of it comes out. This should leave a negative impression in the plaster which is the same as the original clay sculpt:

The best way to get the clay out is to dig the middle out and then work around the edge pulling the clay away from the plaster. If you're lucky it might all come out in one go, otherwise you'll have to go and clean the rest of the clay out, nevertheless, it should separate from the plaster quite easily:

The plaster piece is now your mould to make the latex rubber piece from. Be very careful with the mould as it is likely that the clay sculpt was destroyed as it was removed. The plaster mould is all that is left of the clay sculpt which may have taken some time to make. You can use the plaster mould time and time again to make latex rubber pieces from - some people say up to 100 times depending on the type of plaster used.

In this example I have chosen to pigment the latex to make it black, other pigment colours are available and you can also mix them together. The total pigment added to liquid latex should be around 5% - it will appear very light in colour to start with but as the latex dries the colour will get much darker. Here's my latex mixed with 5% black pigment:

For large pieces you can brush thin coats of latex into the mould and let it dry. You can also pour all the latex into the mould and rotate it around to coat all the surfaces. For small pieces you can completely fill the mould with latex, leave it for 30 mins - 1 hour and then pour out the excess. In all cases when applying latex to plaster you'll find that thick coats are easy to build up because the plaster soaks up the water content from the latex.

Make sure you go right over the edge of the main part of the mould - the excess can be trimmed off later and this will help make sure that there is a thick coat right to the edge of the finished piece. In this example a combination of brushing and rotating the mould was used to build up the latex coats. If you have a really big piece to make you may also consider adding layers of cloth after about every ten coats of latex. This will stop the item from shrinking so much as the latex dries and give it a heavier feel, although it will also stop it being as stretchy as it would be if it were made only of latex:

Once around 5 thick coats or more have been built up and it has dried through, you can peel the latex from the mould. You'll notice that the latex has dried much darker than it was when the pigment was first mixed in. Some pieces of the plaster mould may come away and leave white specs on the finished rubber piece - these can be washed of with water and you'll find after two or three times using the mould this no longer happens:

The latex version of the item will of course turn out the same as your original clay sculpt. You can use the plaster mould time and time again to make more items the same in your choice of pigmented latex.

In this case we have also chosen to paint some features on the latex item. The best thing to stick to latex, is more latex, so we have mixed some green pigment with a small amount of latex and painted that onto the item. You could also try other water based pigments mixed with latex such as acrylic paints. As the pigmented latex will always dry darker, you may have to use several coats on dark backgrounds: