I am having my garden paths resurfaced and one of the options is to do something with the old coal chute. Currently this has an old iron plate cover, which when lifted reveals a 12"x12" square hole with a 45 degree slope into the cellar. What I'd like to do is replace the iron plate with a piece of strong think glass to let some light in. The glass would be worked flush into the path surface and sealed.
If anyone here knows Halifax you might remember that on Bull Green there used to be underground public lavatories and the pavements above had a grid of thick glass squares embedded into the paving - strong enough to stand/jump on, transparent enough to let plenty of light in but no way anyone could see in (or out).
I do not know what this sort of glass is called.