Silicones & Mold Making (Aussie Specific)
The second most common question I get asked by newbie dice makers is where to find decent dice molds. Whilst you can buy pre-made molds these days anywhere from Wish (please don't buy these, they are notoriously difficult to use and also the design is stolen from Dispel Dice) to Etsy, they can vary vastly in quality and unless you know exactly how the mold was made (i.e. was it cured under pressure and if so, what PSI?) then you may run into more problems than not.
The good news is that making your own molds is extremely simple, and you don't need to fork out for expensive custom master dice to learn the basics. My first dice molds were made using a set of cheap metal dice from eBay, and whilst I wouldn't recommend selling dice made from these (due to possible IP theft—Chessex in particular can be weird about it), they are perfectly fine for learning.
And finally, before we begin, I just want to add that this article discusses the process for a two-part cap mold only. If you want to make sprue molds or any other kind of mold, then this is not something I have experience with and thus do not cover in this blog post.
So where do I start?
The first thing you'll want is some form of container to make your mold in. I really like using a slab mold (which means all of my dice get poured together) but I started out using individual molds, and both have their merits. Whichever option you choose, you will need some kind of casing or vessel to make your mold in.
Cleric's Components have a great range of 3D printed slab and individual mold casings in a variety of shapes and colours, however if you don't want to spend money on specialised equipment when just starting out, then some pieces of PVC piping make a great reusable option. Bunnings stock them in 40mm (for individual molds), 80mm or 90mm (for smaller sized chonks) and 150mm (for slab molds).
Okay, I have my casing. Now what?
The next step is to affix your dice in place! The easiest way to do this is by using a sheet of clear contact film which you can grab for as little as $1.00 from Kmart. Simply grab your mold casing and use a permanent marker to trace a circle around the outside of the casing. This will show you how much room you have to position your dice (if making a slab mold) or make it easier to line up your dice in the centre (for individual molds) once we flip the contact sheet over.
Then, simply peel the backing off, lay your contact sheet down sticky side up and place your dice as desired. You can also use small cabochons placed amongst the dice as 'keys' to help align the caps later on. Position your casing on the outline you previously drew and affix the contact sheet in place. I find it easiest to just fold up the edges and wrap the thing in a layer of tape but if you're more patient than me, you can use a hot glue gun to seal the join between the contact paper and the casing instead.
Choosing the right silicone for your mold.
The next step is to pour the silicone... This may seem daunting as there a so many different kinds of silicone available on the market and finding the right one without a recommendation may feel impossible. Fortunately, that's exactly why I am writing this guide and I am going to run you through the pros and cons of some different brands of silicone I have personally used so you at least have a starting point for finding what works (or doesn't work) for you.
The first thing you need to understand about silicone is the numbers or shore hardness. The higher the number, the firmer the silicone. For dice making, we want to use a mid-range silicone so usually something in the range of Shore 20. This is firm enough that it isn't going to warp or buckle when we put them under pressure, and also soft enough that you're not going to destroy your hands (or your brand new molds) trying to get your dice out of them.
Vario 15 from Barnes is a great starting point for new dice makers for this exact reason. It is a little on the softer side but it holds up well under pressure and is very simple to use with a long pot life (i.e. how long after mixing it lasts before starting to set) that will allow you to take your time whilst learning, especially if you've never used silicone before. The only downside to Vario 15 from my experience is that in winter (even in Queensland) it can take a full 24 hours to fully set but you can get a product called Catalyst F to speed up the curing process. You can also mix it with Vario 40 to make a custom blend at a higher shore hardness if you prefer. Simply follow the directions in your technical data sheet for both of these modifications.
The next silicone I like to use is Dragon Skin 20 which is part of an American brand called Smooth On. You can find a variety of Smooth On products imported by a South Australian company called Rowe Trading if you're curious about some of the other silicones our US maker friends use, but I've personally only tried DS20 or Mold Max (which was awful). Dragon Skin 20 is a little firmer than Vario 15 (as the numbers suggest) but it is a great option as it cures in about 4 hours but still has quite a generous 25min pot life, which makes it excellent for a quicker turn around in mold production without the stress of dealing with a faster setting silicone. Just be prepared for an arm workout whilst mixing it... DS20 is thick.
The final silicone I am going to recommend in this blog post is a fast set silicone called Transil (or Pinkysil which is the same product just not translucent) which you can also find at Barnes. This is a Shore 20 silicone and I want to stress that it is fast. The product data lists the pot life as 6mins with a curing time of 1 hour however in the height of the Queensland summer, I find the pot life is about 30 seconds and the curing time closer to half an hour. I love this silicone for making caps (the last stage of our mold making process) but I must stress again that this is not a beginner-friendly silicone and I would not recommend it for someone still learning. Transil is also quite pricey so if you are looking for a cheaper, fast-setting alternative then the Fast 20 from SiliCreate is a great option though I do find it can sometimes not set properly where it touches certain tapes, so make sure you test it with your contact film before use.
Once you've selected your silicone, follow the directions for mixing and simply pour it into your mold container. You want to cover the dice completely but don't make the base too thick as it can make the dice difficult to remove. Going too thin can also cause warping or damage to the mold when removing the dice. A buffer of about 0.5cm over the top of your dice should be fine.
Cure your dice in your pressure pot at roughly 10-15 PSI above what you cast your dice at. I like to use 45psi for molds and 30psi for my dice, but play around with what works best for you.
Making the caps.
Once your mold bases have cured, peel off the contact film and remove the dice from their casing. It may seem obvious to say, but don't remove the dice from the mold yet! We still need them in there to pour the caps.
You can use a hobby knife to cut out some small notches to act as keys to align your caps better if you wish, and you can also use a cuticle trimmer to clean up the edges of the mold if you want for aesthetic purposes but it makes little difference to the mold function.
When you're ready to pour the caps, use a small paintbrush or a q-tip to smear a thin layer of vaseline on the surface of the mold around the exposed dice faces, trying to avoid getting any on the dice themselves. The vaseline layer doesn't need to be too thick, it is just to stop the caps fusing to the bases during the next step and is a cheaper alternative to mold release. You can also use talcum powder but I've personally never tried this method.
Make sure you get vaseline into the grooves of your keys as well, and spread a little around the edge of the mold to help it slide back into the PVC pipe, or simply clamp it back in place around the mold with enough room to pour the cap if you are using the 3D printed casing.
Mix your silicone again and pour your caps at about 0.5cm thickness for individual molds, or between 0.75cm and 1cm for slab molds. You don't want to go too thick as it can make the lids a little difficult to position when pouring, but again feel free to experiment with what works for you. Cure in your pressure pot at the same PSI you used to make the bases.
Once your caps are cured, remove them and the bases from the casing and feel free to give them another trim if you like. Then gently remove your master dice from the mold and give it a clean with either some isopropyl alcohol and a cloth, or I just use baby wet wipes.
There you have it, you've made your very own dice mold! Easy, right?
Some final words.
Depending on how rough you are with your molds and how often you're using them, you should get anywhere between 15-30 pours from a mold before it needs to be replaced. Silicone does degrade and you'll definitely notice it starting to when your dice lose their shine on de-molding, or if some of the silicone starts to stick to your dice. Simply repeat this process whenever you need new molds, and you'll eventually get faster as the process becomes more familiar to you.
All of the silicones mentioned in this guide are platinum cure silicones. If you are using 3D printed master dice, you may run into cure inhibition issues if they haven't had time to fully degass. I recommend getting masters from someone like Cleric's Components, who use a Form 3 resin printer that doesn't have issues with cure inhibition in platinum silicones. Otherwise, if you are using any other 3D resin printer then you may want to try using a tin cure silicone instead. You can get these from Rowe Trading though I have zero experience with them and cannot advise you any further.
And finally, always be gentle when removing dice from the molds! There is nothing worse than making a crisp, perfect mold only to have a number tear out the first time you pull your dice from it, or a chunk of silicone tear away from the edge. The kinder you are to your molds, the longer they will last you.