With the copper foil method of stained glass, precision is needed to make everything come together perfectly. Although foiling can sometimes feel mundane, it is an extremely important step in the process.

Copper foil is placed around all edges of each piece of glass and pressed down along the front and back. Since solder will stick to copper and not to glass, this is a necessary step to allow the assembly of your project in the soldering stage.

Just as a foundation creates a sturdy surface on which a house can be built, the foil becomes the foundation for the solder. As such, there are some key points to keep in mind:

Apply your foil evenly along the edges, ensuring that there is equal coverage on the front and back.

This is as important as making sure that all of your pieces fit together precisely when you were grinding. Remember that solder will only flow and stick to copper (not glass,) and take the following examples into consideration.

 In each of the four examples below, the 7/32" foil was intentionally placed either centered, with more foil on the front, or less foil on the front. Across the bottom of the photo are the exact measurements of the width of each seam.   Despite all of the glass pieces fitting perfectly against each other, the placement of the foil on both halves have altered the width of the seams from 1.5mm all the way up to 4mm!  

The following image clearly demonstrates how important the placement of the foil is when it comes to the size of the center seam.

When folding the front and back edges down, it’s is helpful to do this in a tidy fashion.

Press or crimp the edges down first. If you come to a corner (not a rounded curve), press one side down tightly into the corner, then fold the second side down over the first. This prevents crinkling in the corners and also ensures that the foil creates a nice clean corner where the foil edge meets the glass.

By having the foil edge reflect the exact shape of the piece, you’ll end up with nice, clean, crisp solder lines once your project has been assembled.

Using a burnishing tool (ie. fid, wooden stick, marker...whatever you prefer), carefully burnish all of the edges down until they are smooth. Keep burnishing until all crinkling has been removed and all edges of the foil have well adhered to the glass. Areas that are not well adhered will allow flux between the glass and foil causing loss of adhesion.

Once you’ve foiled all the way around the piece of glass, allow the foil to overlap about ¼” to ½”.

Anymore overlap than this is not helpful. In fact, by overlapping too large of an area, you may find that your pieces don’t fit together well. That’s because you now have a double thickness of foil in a larger area. If you have a nice tight fit between your pieces before foiling, and then overlap too much on many pieces, this can change the way everything fits together and cause some major frustrations.

Try working from the center out for suncatchers and from one corner out for panels.

This will allow you to check the fit properly after each piece has been foiled. If you notice that the glass portion is starting to expand past the pattern lines, you can grind a few pieces where you are which will allow you to adapt the fit as you go. If you foil all of the pieces and then try to fit your project together, there is potential for it not to fit together well at all, at which time you would need to start removing foil in order to grind the glass to fit. I often use the analogy of hair to explain the problem of the ever-expanding project. Often, hobbyists will notice that foiled projects fit differently than they did before they were foiled, and they're right. It will always fit slightly differently as the foil takes up a hair width of space. You won't notice it as much on a suncatcher with only 12 pieces, but start working on a panel with 100 pieces and you'll quickly see a difference. This minor variance of one hair width will compound with the higher number of pieces in your project as there will naturally be more copper foil taking up space. Think of it this way, one hair width is barely noticeable, but the width of one hundred hairs will make you take notice.