I recently had a go at resin moulding and enjoyed the process. After trying out a few bought silicone pendant moulds, I thought it would be fun to make my own!

I chose the Deathly Hallows symbol for my first attempt because it is recognisable but also a fairly simple shape.

This was a multi-part project in which I designed and 3d printed a mould, which I used to make a silicone mould, which I then used to cast the resin pendant.

I had previously designed moulds to make silicone tires for robots, so I knew that Parts 1 & 2 would work, but Part 3 was an experiment. I had no idea if the resin would play nicely with my homemade mould, and I was slightly concerned that the silicone I was using was too soft, so would deform when I added the resin.

Happily, it worked as planned, and I'm so pleased with the final result. It isn't perfect, but I've learnt some new tricks and have a cool new pendant!

Supplies

Part 1 - 3d printed mould

CAD package (I used Fusion 360)
3D printer (I used a Robox)
Filament (I used Robox Chroma Green ABS)

Part 2 - silicone mould

2-part silicone (I used DWR plastics 1-2-1 EasyMould soft)
2x measuring implements (cups, syringes or spoons)
Bowl for mixing
Stirrer

Part 3 - moulding the resin

Gloves
Something to protect your work surface e.g. a baking sheet
2-part resin (I used Pebeo Gedeo Crystal Resin)
2x measuring implements (cups, syringes or spoons)
Bowl for mixing
Stirrer
Resin dye (I used some generic dyes from AliExpress, but I recommend getting something decent)
Something to cover your work while it cures

Part 4 - making the pendant

Eye pin or wire loop
Wire cutters
Pliers
Lighter
Chain / ribbon / keyring etc

Step 1: Designing and Printing the First Mould

The intention here is to design the shape of your final pendant, then surround it with a wall, so that you can make an inverse silicone mould.

Here is the process I went through, using Fusion 360, to get a design I was happy with:

I drew a sketch of the symbol in Fusion 360, then added the wall around it (Picture #1).
I extruded the symbol and the wall (Picture #2), then made a new sketch from this body, to make the base (Picture #3).
I extruded the base and joined the bodies, to make a complete mould shape (Picture #4).
To save on plastic, and make it a neater shape, I then chamfered the edges of the wall (Picture #5), then filleted the whole piece, to give a nice rounded edge on all surfaces (Picture #6).

My design finished, I 3d printed it with 30% infill (Picture #7). It didn't need support, but as I was using ABS I added a brim to help with bed adhesion, as it wouldn't affect the important parts of the mould.

I noticed later on in the project that you can see an imprint of the 3d print lines on the finished pendant. My current idea to fix this is to treat the ABS mould with acetone vapour, to smooth out those lines, before making another silicone mould. There might be better ways of doing it / ways that would work with a PLA print, such as coating it in something.

My mould design is attached. You can also find this design, the symbol alone, and a non-inverse mould design, on Thingiverse: https://www.thingiverse.com/thing:3689082

deathly_hallows_mould.stl
Download View in 3D

Step 2: Creating the Silicone Mould

Gather your supplies for this stage (Picture #1), and check the instructions on your silicone to see how much of each part you need for it to cure. Mine requires equal parts of A and B.

I have two syringes that I use each time, to make measuring easier, but you could just as easily use spoons.

The Deathly Hallows mould takes 16ml of silicone mixture to fill. If you are using the same silicone as I am, put 8-10ml of part A into your bowl, then add an equal amount of part B to it.

If you are using your own mould design, fill it with water and empty it into a measuring cup to work out how much silicone you will need to make.

Stir it carefully with a stick. You want to mix the two parts together fully, but not introduce bubbles into the mixture. (Picture #2)

Pour carefully into the mould, pouring slowing will keep the number of air bubbles down. (Picture #3)

Pour until the brim of the mould - it will dome slightly at the top. (Picture #4)

Now leave to cure, following the instructions on your silicone. Mine says 1-2h, and it was ready in 1h. I keep an eye on the bowl that I mixed in, and once I can easily peel the remnants out of it, I know my main design will be ready as well!

Once it has cured and turned solid, carefully pull it out of the mould by pulling from one corner - it has some resistance at first, but once you have a bit out it is easy to remove. (Picture #5)

You now have the finished silicone mould, ready to fill with resin! (Picture #6)

Step 3: Moulding the Resin

Safety: Resin is not as nice to work with as silicone! Work in a ventilated area, wear gloves and cover your work surface. I use a reusable baking sheet, which the resin doesn't stick to.

Gather your supplies for this stage (Picture #1), and check the instructions on your resin to see how much of each part you need for it to cure. Mine requires two parts A to one part B.

My resin came with two measuring cups, so I use these, but you could use syringes or spoons like with the silicone.

The Deathly Hallows mould takes 5ml of resin mixture to fill. My measuring cups are fairly large though, so to make it easier to measure accurately, I made up 15ml and used the rest up in some other moulds.

If you are using the same resin as I am, put 5ml of part B into your bowl, then add 10ml of part A to it. (If you have smaller measuring cups or syringes, then make less resin mix than this!)

Stir it carefully with a stick. You want to mix the two parts together fully, but not introduce bubbles into the mixture. (Picture #2)

Once it is mixed, add a drop of dye and mix thoroughly - add a drop at a time until you are happy with the colour. I added a nice Slytherin green! (Picture #3)

The soft silicone mould was hard to move without spilling, so make sure that you pour the resin in a place where you can leave it to cure, or do it on a tray or something.

Pour carefully into the mould, pouring slowing will keep the number of air bubbles down. (Picture #4)

A perfect amount of resin will dome slightly at the top; I went a bit too far and broke the surface tension (Picture #5), but it's better to pour slightly too much than too little as it shrinks as it cures, and you can cut or scrape off the excess in the next step. If you don't put enough resin in, your final piece will look concaved, with the middle lower than the edges (Picture #6).

Now leave to cure, following the instructions on your resin. Mine says 24h, but it took closer to 48h to become fully solid (you want to move on to the next step before it is fully solid).

Cover your resin with something to stop dust sticking to it - I used a plastic takeaway tray - and wait. (Picture #7)

For the next step, you want to add a pin before it has fully set. It should be solid enough to keep its shape, but soft enough to push a pin into. For me, this was about 24 hours.

I recommend buying some less cheap dye than I used! A few dark swirls appeared after it had been sat for a while, so I merged them back in with a pin a couple of times while it was still very liquid. If you don't, you end up with patches in the finished design (Picture #8), so keep an eye on yours.

Step 4: Creating the Pendant

Gather your supplies for this stage (Picture #1).

When you are confident that your resin will not deform, put on some gloves (to save it from fingerprints), and peel away the silicone mould. (Picture #2)

I first tried to remove it 21 hours in, but it was very bendy still, so I pressed it back into the mould so I wouldn't damage it. I continued after 24 hours. I would ideally have waited longer as it was still very bendy, but it was getting late so I risked it!

The soft silicone I used for my mould was much easier to remove from the resin than the harder silicone of my bought moulds, so it was much easier to get in and out of!

If you have any excess resin on the edges from overpouring, trim or scrape it off now, before it gets too solid. I got lucky, so don't have a picture of this step.

Cut the eye pin to the right length - it will be visible through the clear resin pendant, so I cut mine short. (Picture #3)

Holding the pin by the eye with pliers, heat the pointy end with a lighter - this allows it to enter the resin without pushing at it and deforming the shape. (Picture #4)

Using a twisting motion rather than forcing it, push the eye pin into the resin pendant until it is all the way in. (Picture #5)

My pendant was too bendy, so it deformed the top slightly. It's not too noticeable but, ideally, wait until the resin is less bouncy to get a cleaner edge. The same issue meant that the pendant twisted slightly while I was handling it, so I flattened it under some books to straighten it back up again.

Put the piece back under your dust cover until it is completely solid (I left mine another 24 hours).

Now your pendant is ready to attach to a chain, ribbon or keyring! (Picture #6)