You should realise that when making moulds and casting them, you get what you pay for. If you want high quality exact replicas then you need to shell out for those higher priced materials like liquid silicon and model making resins.
If, like me, you don't have easy access to the proper materials (I'm in the Philippines) or simply don't want the expense then this instructable is for you :)
Original toy - This is the toy or object that you want to duplicate. This instructable will only work for objects which have a flat back. I used a plastic model of Haibo, the mascot for the 2010 Shanghai Expo.
Plaster of paris - I bought a small pack from a local hardware store. There are recipes online to make it at home with common kitchen products.
Two piece resin - I bought a cheap two part plastic resin from a local hardware store. It's meant to marine applications and gluing objects together. It was 70 PHP (1GBP/1.5USD) for a reasonable amount.
Clay - Any basic cheap modelling clay will do
Sandpaper - Depending on your resin and your mould, there'll be an amount of sanding required.
Paints - I used acrylic paints and an acrylic laquer.
Step 1: Prepare the Toy for Mould Making
- 1) The toy you want to duplicate
- 2) Some clay. I'm using cheap modelling clay
- 3) Petroleum jelly or other lubricating material
1) Since this is a one part mould, the object you want to duplicate should have a flat back. Because the object I chose doesn't have a flat back, I pushed it slightly into the clay and when I cast it later, it will come out having a flat back.
2) Roll out some clay and place your object on top. Ensure there's a border of clay around the object that you can later make a box around to hold the plaster while it sets. Push your object slightly into the clay to ensure that no plaster can get under it when you pour it in later.
3) Apply a coating of petroleum jelly or other lubricant to the object and the surrounding clay. This will ensure you can remove it from the plaster mould later. This step is vital.
Step 2: Create Box for the Mould Pouring
Remember, plaster is a reasonable thick liquid when mixed, so it doesn't have to be a perfectly waterproofed box!
Step 3: Mix Plaster and Pour
Pour the plaster mix into the corner of the box rather than directly onto the model. While pouring, try keep a thin steady stream pouring in until you've filled about 3cm or so above the model. This should hopefully avoid any air bubbles being set in your mould.
Leave the plaster to set. The brand I use sets reasonably hard in about 30 minutes but I usually leave it an hour or two. For the strongest cure, you should leave it over night.
Step 4: Remove Toy From Mould
Remove the cardboard and turn everything upside down.
Peel away the clay, if you're lucky your toy might come out with the clay.
If the toy hasn't come out with the clay, carefully remove it anyway you can.
Usually I can get the toy out without too much work. If you have difficulties then consider hot glueing something to the back of the toy and using that to pull it out gently. Then just remove the hot glue.
Step 5: Mix Plastic Resin and Pour Into Mould
1) The first thing to do is apply a layer of petroleum jelly or other lubricant to the inside of the mould and the top. This is a crucial step, if it's skipped then the chances of getting the duplicate out without breaking the mould are very slim.
2) Mix the resin. I'm using a very cheap, two part plastic resin which is meant for marine applications and glueing objects together.
Follow the directions that came with your plastic resin. For me, I simply had to mix an equal(ish) part from tin A and tin B.
3) Pour the resin into the mould. The resin I used is quite thick when mixed. I imagine you'd get better results from a thinner resin since it would flow into the mould easier.
As you can see in the picture, I simply scooped the resin into the mould. I wasn't all that tidy but it's not so important since the resin becomes a little runnier after sitting for 5 to 10 mins and smooths itself out.
4) Wait for the resin to cure/harden. How long the resin takes to cure will vary hugely between brands and room temperature. Mine takes about 3 hours in a hot room for the initial cure and 12-24 hours for a solid cure.
Step 6: Remove Resin From Mould
I usually remove the cast from the mould after about 2-3 hours. The resin is hard enough to remove from the mould but soft enough to trim with scissors or a hobby knife. The time will vary between brands and room temperatures.
Once you've trimmed most of the extra resin away, leave it overnight to fully cure/harden.
Step 7: Tidy Up the Cast
Sand it down to a smooth surface and get your paints ready. I applied several coats of acrylic paint and finished it with a few coats of acrylic laquer.
That's it, you're done!