Tools you will need:
A laser cutter / etcher
Vector editor software (i.e. Inkscape)
A cutting board with an angle measurement
A glass scorer
Score running pliers for glass (optional, but recommended)
A soldering iron
A small brush for the flux
An icosahedron jig
Materials you will need:
A sheet of stained glass (12" x 12")
A scrap piece of cardboard (roughly 11" x 11")
Adhesive backed copper foil
Once you have gathered everything that you need move on to the first step. If you don't have a laser cutter the last step includes options for adding the numbers in other ways. Also, since a lot of people have been asking in the comments, these, along with other art, can be purchased from B&B Glassworks (http://www.bandbglassworks.com)
Step 1: Making the Cardboard Template
The next step is to put numbers in each triangle. Here you can use any font that you like but remember that the top of the numbers always face a point of the triangle. Also, if you're going to etch on the back of the glass, like we did, you need to remember to mirror your numbers so they show up correctly on the front.
Now send this to your laser cutter and let it go on your sheet of cardboard. If it etches the numbers in the cardboard that's ok, we're not going to use those pieces for anything anyway. What we want are the holes that are left behind.
Step 2: Preparing the Stained-Glass Triangles
Once you have 20 good pieces we can etch the numbers on them. Place each triangle in one of the holes of the cardboard template on the laser cutter's cutting surface. Now you can use the same file that we used to make the template but be sure to set your laser to etch only! We don't want to cut around the holes again!
Step 3: Putting It All Together
At this point you may want to consult a d20 or get some really good pictures from the internet, because the location of the numbers is very important.
Choose the first five triangles you will be using and place them face-down in the jig making sure that they are evenly aligned and that the flat tops of them form a continuous flat plane. I’ve found it best to brush some flux in the bottom of the little bowl that the triangles make before aligning them, then melt some solder so it drips on the spot where all five points come together. That will hold them firmly in place while you solder the other seams. Once you have all the seams soldered on the inside for the first five pieces, rotate the glass in the jig and add additional triangles and solder them in place on the inside.
Solder all the triangles together except for the last five pieces. These pieces will make a “lid”, so once you are done you should have a 15 triangle bowl and a five triangle lid, both of which are soldered only on the inside. Now, flip them over and solder the seams on the outside keeping the bowl and the lid separate. Once you have all the outside seams soldered you can clean the pieces with soap and warm water to get the flux off the inside. The last step is to place the lid on the bowl and solder it in place, then clean it again with soap and warm water and you are done! Congratulations!
!! Important !!
While soldering the pieces together be sure that you are putting the correct numbers next to each other!
Step 4: What If You Don't Have a Laser Cutter?
Chemical Etching is a common technique used to etch glass. The result is usually more of a frosted look than what you would get with the laser cutter but it is still a nice look. There are several Instructables that will show you how to do this and get very nice results. I would recommend etching the pieces using the chemical process at the same point as you would use the laser cutter because it will be much easier to do while they are still flat.
Sand blasting would work in much the same way as the chemical etching process. You would mask off the areas that you want to remain intact and they would be protected from the sand. Sand blasting can be adjusted to get the look that you want. It can be anything from a light frost to even deeper results than the laster cutter.
Your local craft store contains a wide assortment of vinyl stickers that you can use to add numbers to your d20. The adhesive will be affected by the heat from the soldering iron and the flux so I would recommend that you completely finish and clean the d20 before sticking the numbers on.