To try out the silicone and resin I bought a while ago, I made a recast of a Nendoroid head. Recasting of existing figure parts is often done by people who modify figures, to avoid destroying the original parts. It’s the same technique that can be used to produce your own garage kit from original figure sculpts.
I got my silicone and resin from a web shop in the Netherlands called Silicones and more, which has pretty cheap materials as well as cheap shipping within Europe. Buy your stuff wherever you can find it cheap.
Let’s get started. First we need to make a box around the part we want to recast. There are a lot of people who make their boxes out of fancy hard plate materials with a lot of effort put into making the edges watertight. I folded a box out of paper. Don’t make it too large, you’d just be using more silicone than needed, which is a waste of materials. The model is placed with an unimportant side downwards, and in a direction that allows any air to escape when filling the box with silicone.
The silicone I used for this sample is the Yellow Shore A 25. This is a 2 component silicone with a 1:1 mixing ratio, which is really easy to work with, as you can pretty much mix it on sight. The Shore 25 refers to the hardness of the silicone, the color is arbitrarily added by the manufacturer to one component to make it easier to see if your silicone is properly mixed.
After mixing the two components together, you have about half an hour to work with it, so you can take your time. Pour the silicone very slowly in a thin line into a corner of your box, this way the bubbles in the mixture are pretty much removed. Pour slowly into any small cavities, such as the connector in this case, and then just fill up the rest. Any bubbles will go upwards, so only surfaces pointing downwards are at risk of trapping them.
Then you wait 4 hours, or whatever your silicone supplier gives for demoulding time.
Remove the box. The paper is a bit sticky but comes off easily, the silicone is solid enough to stay in shape by itself.
Pull the silicone open, and use a knife to open it further so you can pull out the model. Be careful not to cut into your model, pull the silicone away from the model while cutting. You can use force, the silicone won’t tear apart by itself. It’s not necessary to cut the entire silicone mould into two separated parts.
The silicone does not damage the original model, and releases the model without the need of any release agent. I had some unhardened silicone restants in some areas of the model, though, I suspect I did not mix the silicone long enough, not a critical issue though, as it’s not in visible places luckily. The inside of the mould looks perfect, and doesn’t have any large bubbles. A large bubble would result in a small blob sticking out after the cast. There are some small bubble visible, though, which will cause small bubbles to appear on the casts, as the resin is too thick to get in there.
Next is the casting itself. I’m using the D70 Ultra Fast Polyurethane (or PU), which is also mixed in a handy 1:1 ratio. Make sure to get a resin that is at least rated to cast as small as 1mm.
Close the mould, the parts that were cut will just stick together perfectly by themselves and will only form very minor seams, no need to bind it together. Mix the resin according to it’s instructions. I simply guessed the needed volume on sight, it ended up being just as much as I needed. Pour the resin into the mould.
Ventilate the room. Seriously.
After the demoulding time is passed, pull the model out of the mould. You may use force. Make sure none of the spillover resin breaks off and falls into the mould, as it will stick to the sides.
There’s not really any notable shrinkage on these resins. The recast fits perfectly.
There are some bubbles in the resin in some places where they could not escape. I should’ve held the mould at a few angles to let the air escape.
On the side of the face there was an issue with the mould silicone not having hardened completely, so the surface there is bad. This is probably where I had spilled the first drops of silicone as I was pouring, which came from the edge of the mixing box, so they likely did not get fully mixed.
The bubbles in the surface are caused by working too fast. The resin components I use have to be shaken before usage, as some of the chemicals sink down, but I should have waited for the air to get out again before using it. Other than that the cast is pretty good for a first try.
The connector hole is cast perfectly.