This article presents an approach for creating and using a customized, single-use 3-dimensional pattern so that you can be creative with the shape of your glass.

You will need:

Corrugated plastic, aka coroplast (the stuff that looks like plastic cardboard, not the big stuff people use for roofs)
Box cutter or x-acto knife
Scissors
Ruler
Tape (I prefer gaffer’s tape, but duct tape works as well-it’s just more of a pain to take off repeatedly)
Spray foam insulation (I use Great Stuff brand “door and window” insulation. The brand probably doesn’t matter but the “door and window” DEFINITELY does. Non door and window will burst your seams.)
Cooking spray
Water in a spray bottle
Tin foil or plastic sheeting (to protect your table)
Nitrile/rubber/latex gloves
Clothes you don’t care too much about
Acetone nail polish remover
A large pipe cleaner
A bamboo skewer
Felt-tip pens (ideally in multiple colors, but if not, black is good)
Work gloves
Table spike (see step 5)
Tools for cutting glass, foiling, and soldering glass (I’m assuming you already know how to do this and have your own preferences for specific tools and techniques)
Sand paper (any grit)
Bolt cutters
Copper or steel rod (⅛" or 3/16")
Pliers
Vise (optional)
Flux (if you are working with steel, it must be Stay Clean Brand)

Step 1: Make a Plastic Model of Your Piece

For this step you will need:

Corrugated plastic, aka coroplast (the stuff that looks like plastic cardboard, not the big stuff people use for roofs)
Box cutter or x-acto knife
Scissors
Ruler
Tape (I prefer gaffer’s tape but duct tape works as well, it’s just more of a pain to take off repeatedly)

First, make a model of what you want the final piece to look like. This is honestly mostly trial and error, much more than the rest of this tutorial. I start by cutting out a shape that I think will be about right, score and fold it, and tape it together. Then I start shaving down pieces that are too large, replacing pieces that are too small, and frequently replacing whole sections of the model that didn’t come out the way I had expected.

If your model is symmetrical, you can make one half, then dismantle it, trace it, cut out the other half, and assemble the whole thing.

Step 2: Make a Foam Mold of the Interior of the Model

You will need:

Spray foam insulation (I use Great Stuff brand “door and window” insulation. The brand probably doesn’t matter but the “door and window” DEFINITELY does. Non door and window will burst your seams.)
Cooking spray
Water in a spray bottle
Tin foil or plastic sheeting (to protect your table)
Nitrile/rubber/latex gloves
Clothes you don’t care too much about.

Steps:

Lay out the foil or sheeting on a surface and place your model on it. Make sure to do this somewhere that you can leave it undisturbed for 24 hours.
Shake up the spray foam.
Spray a bit of the foam into the wastebasket to make sure that it is making a convincing foam.
Spray the inside of your model thoroughly with cooking spray.
Lightly mist the inside of your model with water, to put a layer of water over the oil.
Fill the inside of your model with foam.
Go immediately to the next step (if you don’t, you’ll have to throw out your leftover spray foam).

Step 3: Storing the Spray Foam So That You Can Use It Again

You will need:

Acetone nail polish remover
A large pipe cleaner
A bamboo skewer
A box cutter

If you let spray foam set in the aperture of the can, you will have to throw out the can, so it’s important to take the following steps immediately after using it. Don’t take your gloves off till you’re done.
Unscrew the removable spray tube
Pour acetone into the threaded tube at the top of the can.
Cut a 2” long section of bamboo skewer using your box cutter against a table. Dip the bamboo section in acetone and stick it down the threaded tube in the top of the can. Leave it there until the next time you use the can. Store the can upright so the bamboo doesn’t fall out.
Put a slight bend in the tip of the pipe cleaner as pictured.
Cover the pipe cleaner in acetone.
Feed the pipe cleaner, bent end first, into the threaded end of the removable spray tube. It will take a bit of finagling, but you should be able to get the pipe cleaner to go around the corner and all the way down the spray tube. Futzing with the bend at the tip will help if you’re having trouble, as will making sure that your pipe cleaner is really really soaked in acetone. Leave the pipe cleaner threaded through the spray tube until next time you use the spray foam.

If you got spray foam on anything during this, clean it up with acetone before the foam sets.

Step 4: Remove the Plastic Covering From the Foam

You will need:

Felt tip pens. Ideally in multiple colors matching your glass, but black is sufficient.
Boxcutter

Wait 24 hours from when you sprayed the foam. The can says 8, but you will be accessing the parts of the foam that are not exposed to air, and these take longer to cure.

Take the plastic off carefully; it is easier if you can remove a single segment of plastic at a time. This will not always be possible; you’ll be limited by how you constructed the model. As you remove them, mark your panels with letters, and mark the faces of the foam piece underneath with the matching letters. After you remove each panel, trace its outline with your marker onto the foam. If you had to remove several panels at once because you had scored and folded, cut the panels off one at a time, then place the remaining panels back onto the foam so that you can trace the outline of each removed panel. Alternately, if your angles are fairly sharp, you can just trace them with the pen without using the panels as a guide. One way or another, get the panels traced onto the foam, removed and separated. Save these plastic pieces for the next step.

Step 5: Cut Out the Glass and Solder It Over the Mold

You will need:

Work gloves
Table spike (see below)
Tools for cutting glass, foiling, and soldering glass (I’m assuming you already know how to do this and have your own preferences for specific tools and techniques)

This step assumes that you already know how to make flat stained glass, and that cutting, foiling, and soldering glass are familiar concepts. If this is not the case, please go read another how-to on introductory stained glass. A good one can be found at https://www.instructables.com/id/How-To-Stained-Glass/

You will need some sort of metal spike to stick your model on. The simplest way to make this would probably be a large nail stuck through a board. Mine is a long piece of 3/16” steel bent and sharpened. You might also be able to use a restaurant check spindle, although I have not tried this.

Pick two adjacent plastic panels (the ones you cut out), trace them onto glass, cut them out, and foil them.
Spike the foam model with the seam between the panels you have chosen facing up.
Flux the edges along the seam.
Put a work glove on your off hand.
Hold the panels on the model with your off hand.
Set a bit of loose solder on the seam.
Melt the solder to attach the panels together.
Pick up the solder spool and solder the top of the seam.
Take the pair of panels off the model, flux and solder the inside of the seam.
Using a boxcutter, cut away the top of model where the panels sit, to make space for the solder seam you’ve just created (see image).
Pick another panel that is adjacent to the ones you’ve done and repeat to complete the model, MAKING SURE TO LEAVE A SEAM TO REMOVE THE FOAM FROM THE MIDDLE.
Remove the foam and solder the final seam. You won’t be able to solder the inside of this seam, unless your design has gaps in it.

Step 6: Support Struts (optional)

You will need:

Sand paper (any grit)
Bolt cutters
Copper or steel rod (⅛" or 3/16")
Pliers
Vise (optional)
Flux (if you are working with steel, it must be Stay Clean Brand)
Soldering iron
Solder

Depending on your design, it may well involve some rods for support. If not, feel free to skip this step. I’ve used both steel and copper for this. Copper is easier to work with, but steel is stronger.

Using pliers and/or vise, bend your strut into your desired shape. Sand your strut, flux it (using Stay Clean if it is steel), and then coat it in solder, making especially sure that the parts of the strut that will attach to your piece are well-coated. You will have to spend more time getting the metal hot than you would have to when working with foil. Solder your strut to your piece. Note that the seams of your piece are stronger than the edges. For small struts, you may have to be somewhat clever to hold the strut while soldering it. Pliers can help. In some cases, it can be helpful to temporarily solder a secondary rod to your strut to support it while you are soldering (pictured). Make sure that your secondary strut is far enough from your joint that you can remove it without melting your joint.