Plating
Plating or Layering, also mistakenly called Overlay, not to be confused with Plate Glass or Electro/Chemical plating.
This is where two or more pieces of glass are assembled together into a stack by soldering them together. Often used to get colors or textures that don't otherwise exist and to add depth. Plating is not limited to either Foil or Came as both can be stacked with varying results.
Uses
Plating is an advanced technique often not used in most windows due to the complexity it add along with the weight. It also requires a fair bit of planning ahead to use correctly so parts are properly supported and the look of the glass ends up as desired.
Creating Textures
Due to Texture being created at the factory, if a color and texture combination can't be found it's possible to take the texture in clear glass and plate the desired color behind it to make it look like the desired texture.
Creating Colors
As glass is a rather complex material lots of colors or color patterns don't exist, plating can step in and allow people to create colors or color designs that otherwise wouldn't exist.
Issues with Plating
With the nature of how these stacks are assembled there's a few limitations and other issues that appear with plating that can or can't be solved.
Glass Opacity
As glass gets more and more opaque, you can quickly run into issues with the glass when stacked becoming so opaque that it no longer works as intended. This can be worked around by using more opaque glass near the front of the stack and using less opaque glass in the rear. This will allow the maximum amount of light to penetrate the stack and reach the more opaque front.
Glass Light Losses
Glass isn't perfectly transmissible, there's loss in light passing through it. Thus even a large stack of clear will eventually cause darkening. In colored glass this becomes more of a problem as the color itself obstructs more light. The higher the density of the color the greater the issue becomes.
Index of Refraction Differences
Index of refraction is how much light is bent when entering and exiting a medium that does not absorb the light. Ideally you want materials to have as small of a change as possible or it causes reflections, refractions of the light that will then result in changes in how the next layer interacts with the light. As your layers increase the more of these transitions that exist and contribute to the end result. Most of these will be destructive in nature as it will make the stack look cloudy or lit oddly at different angles.
An easy way to explore this would be to take a chunk of clear glass and a chunk of colored glass. Place the colored glass below the clear and observe it, the less flat the the two sides that meet are the greater you can see how it affects the light. In this stack you have a stack like this air|glass|air|glass|air stack. Now, let's change the middle most air for some water, air|glass|water|glass|air is now the stack we have and you can see how this greatly changes what the stack looks like!
Trapping things between the layers
This is the worst part of plating, because we are attaching two parts of glass together with a gap between them stuff can get stuck between them. Flux, water, chemicals, dirt, dust and whatever else can get trapped between the layers and affect or even ruin the stack. Then requiring it to be tore apart, cleaned and then reassembled before it can be placed back into the project.
Difficulty to repair
Plating introduces lots of issues with Repair as not all the glass in the stack could be damaged thus making it complicated to get to the part that is actually broken without harming the other plates in the stack.