A dice master is a specific type of prototype dice set that contains all the requested graphics and fonts in all the right sizes and places.
Resin, acrylic, PMMA, and other types of plastic dice are traditionally made using molds. These molds are traditionally created using some sort of soft, flexible silicone (or something similar).
In short, handmade mold production is as such: take a set of dice, pour silicone over it, wait for the silicone to cure (I.E. become solid), and then pop the dice set out. At the end of this process, you'll have a big hunk of silicone with perfectly dice-shaped holes in it. Fill these holes with new resin, acrylic, etc. in new color combinations to produce new sets of dice!
I'm sure you can see what the problem with this is. How can you make a mold if the dice set you want doesn't exist yet?
This is what a master set is. These days, masters are usually created using 3D printing. You model a test set, print it, sand it, and use it to create your mold. Since you're only using it to make molds, it doesn't mater what a master set looks like. It can be perfectly clear, a gorgeous shade of blue, a boring matte gray—anything. All that matters is that it's perfectly polished and contains all the right graphics/fonts in all the right places.
Once you have your first mold, you can use this mold to make dozens of masters, and then use these masters to make dozens of molds. But you need one master to start, and getting that first master takes the most time.
Why? Because you have to model it, print it, tweak it if something went wrong, print it again, check it for imperfections, sand it, polish it, and then use it to make a mold. And you'll have to do a lot of this all over again if you accidentally choose a master material that sticks to silicone. If you're outsourcing master creation, you'll also have shipping times, lost packages, and transit damage to contend with.
All this is without even mentioning that mold creation really isn't as simple as "pour silicone over a set of dice and wait"... which I'll get into now. You will have to make a bottom and a lid, and these two parts must fit together perfectly every time. If the silicone you choose is too stiff, you won't be able to get anything out of your molds. If it's too soft, the silicone will bend and flex while your dice are curing inside it, which certainly doesn't produce the result you want, even if the results are interesting.
Most of all, you don't want uncured, liquid silicone all over the place, so you have to pour your molds into watertight containers. Seriously, a thin layer of silicone on the floor is invisible, difficult to get rid of, and wicked slippery. Ask us how we know.
This page is part of our Answers to Oddly Specific Questions series.