This is Part 3 of a series of blog posts on how to make resin artisan keycaps. In this post, I’ll use the hand-sculpted clay master from Part 2 to create a two-part silicone mold for casting resin. In part 4, I’ll make a multi-shot resin artisan keycap using the mold.
Important: Read Part 2 First
Please make sure you’ve read How to Make Resin Artisan Keycaps – Part 1: Getting Started and Minimum Equipment and How to Make Resin Artisan Keycaps – Part 2: Sculpting a Keycap Master before proceeding.
Make a Silicone Mold of a Clay Keycap Master
To make a silicone mold of the Renewal artisan keycap, the first thing I need is the clay master sculpt that I made in How to Make Resin Artisan Keycaps – Part 2: Sculpting a Keycap Master. So go grab yours and let’s rock and roll!
Silicone Mold Containers
You will need containers to pour your silicone into so that you’ll end up with a block of silicone with your mold cavity inside. The sculpting base that I used to make my clay artisan keycap master on in Part 2 is sized precisely to LEGO measurements. This allows me to make containers at home myself out of LEGO. You can do this if you’ve got LEGO on hand, or you can 3D print (or buy) a mold container box. The LEGO space required will be 4×4 studs (or 16 studs square).
Two mold containers are needed to make one complete mold, because keycap molds are two parts: the visible part of the keycap, and the “butt” — the bottom of the keycap where it attaches to the keyboard.
I already have my master for the sculpted (top) part of the keycap. If you’re following along with your own sculpt, next you’ll need a stem cavity master to form the bottom part of the keycap. You can 3D print stem cavities if you have the proper equipment, or you can purchase them. I like to use the Z-butt system. You can order your own stem cavity from ZappyCappys, or you can order a full kit, including platforms and mold container boxes. There are other systems available as well, such as :~$ynth, which you can check out here.
This is also your opportunity to add your maker’s mark. Maker’s marks go in the stem cavity, and you can work with the vendor to get yours 3D printed into your master when you order it (or include your own if you’re printing the cavity master yourself).
Prepare to Make the Mold
Once you have your mold containers, stem cavity, and master sculpt, it’s time to make your mold! At this stage, you will also need the following:
- Paper towels or shop towels
- Disposable gloves
- Mold release
- Foam cleaning swabs (recommended)
- Disposable cups
- Stir sticks (e.g., popsicle craft sticks or swizzle sticks)
- Kitchen scale (recommended or required, depending on your silicone)
- Two-part silicone rubber
- Pressure post (recommended)
Prep Your Mold Masters
To prepare your mold masters, lightly spray your stem cavity and master sculpt with mold release. This prevents the silicone from sticking to the masters and makes removal easier. I like to spray a light coating of mold release on my masters, then use foam cleaning swabs to distribute and remove excess mold release. If you are too heavy-handed with the mold release, parts of your finished mold will have a shinier texture than other parts, which will affect your castings.
Mix the Silicone Rubber
The next step is mixing your silicone rubber. I have a strong preference for Smooth-On Mold Star 30. Mold Star 30 is a two-part platinum silicone rubber that can typically be measured in equal parts by volume. There are also preparations of it that can be measured by weight, so read the packaging.
Make sure to mix each part thoroughly in the container with a stir stick before dispensing.
Measure or weigh equal parts A and B into separate containers.
Next, mix parts A and B together thoroughly. I like to set a timer for three minutes and stir nonstop for the duration of that time.
Pour the Silicone
Pour the mixed silicone rubber into your mold container. You should completely cover your master sculpt, but do not cover the sprues of your stem cavity. Those sprues exist to release excess resin from your mold when you press the two halves together. Without these holes, your castings will fail, so make sure that your mold does not cover them entirely.
Here are some tips for pouring your molds:
- Pour slowly.
- Pour from high up in a thin stream. This reduces air trapped in the silicone.
- Pour into a corner of the mold container and let the silicone naturally flow to fill all nooks and crannies.
Once you’re finished pouring your silicone, you can gently tap the mold container against the table to help release trapped air. The silicone will degas on its own; there is no need to use a vacuum chamber! Give the poured molds a few minutes to degas before placing in a pressure pot (if you have one).
Cure the Molds
If you don’t own a pressure pot, that’s fine: cover your molds so they don’t collect dust or particles from the air. A sheet of paper is perfectly fine for this. Then leave them somewhere they won’t be disturbed for at least six to eight hours.
If you do own a pressure pot, place your molds inside, seal the pot, and pressurize. I cure my molds at the same pressure that I use for resin castings (roughly 45 PSI). Leave the molds inside the pressure pot for the duration of the cure time.
Mold Star 30 should cure for six hours minimum. However, I have found this to occasionally be too short, and I prefer to cure my molds overnight (8-10 hours). Attempting to remove the mold too early will ruin it, so don’t be impatient!
Trim the Finished Mold
Once the mold has cured, you can extract it from the mold container and remove your master sculpt and your stem cavity master. If you’ve allowed the mold to cure for the appropriate time and used mold release, this should be easy. If you have trouble removing your masters, consider where in the process you could make tweaks to change the outcome next time.
Once you’ve removed the masters, you may see something like the photo below. If you look carefully at the mold for the sculpted keycap, you can see some excess silicone flashing around the inside edge.
It is very important that you trim this flashing. If you don’t, when you pour resin into the mold and then close it, it will trap air bubbles inside the mold. If this happens, even a pressure pot will not eliminate those air bubbles. See the photo below for what this looks like.
Once you’ve cleaned up and trimmed your mold, you’re ready to start casting resin and make your first resin artisan keycap!
Stay tuned for Part 4 of this series to learn how to cast multi-shot resin into your keycap mold — coming soon!
I make artisan keycaps, miniature foods, charms and jewelry, dioramas, digital art, and sell things in my shop. I also write blog articles describing my process and showing tutorials, and announce new products, limited raffle sales, giveaways, and more on Instagram and in my email newsletter.