Leica M3 - Variations - Glass vs Metal Pressure Plate
The first Leica M3 cameras to leave Leica's Wetzlar factory in 1954 were fitted with ground glass pressure plates. Sometimes also referred to as "ceramic" plates, these glass plates were chosen for their excellent optical flatness and good wear characteristics. However, Leica's engineers discovered that the glass plates could build up an electrostatic charge under certain conditions that would discharge onto the film, ruining an image. In 1957, Leica switched to steel pressure plates (M3 serial #854000-) that would be used in all subsequent Leica M cameras.
How can you tell if your M3 has a glass pressure plate? Even to a keen eye the difference is minute, but there are a few telltale signs. Glass M3 plates have a small "frame" that surrounds the plate that can brass slightly with age. Glass plates also have a very smooth surface that has no distinct pattern or grain. Metal M3 pressure plates are a single piece with no outer frame, and have a visible lateral grain (thin line-like marks) that run in the direction of the film transport.
If you've got an M3 with a glass pressure plate, don't sweat it -- static discharge issues only come up in extreme conditions like shooting in sub-zero weather. Glass plate M3s are a testament to the amazing lengths Leica engineers went to in order to create the finest photographic instrument the world had seen.
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