I took (actually, my husband T took, while I “windowpaned”) some photos of the stages of gluten development. I hope someone will find these useful. Most of the breads I make call for the gluten to be developed to a medium stage.
Gluten development is tested with the “windowpane test.” Pinch off about two tablespoons of dough and try to stretch it into a thin membrane (windowpane).
If you can do so without tearing, but the membrane is mostly opaque, you have barely developed gluten.
If you can stretch a paper-thin, very translucent windowpane, the gluten is fully developed.
A medium level is in between these two extremes: the windowpane is translucent with some opaque areas.
The progression from minimally to fully developed gluten: