Piezoelectric Quartz Crystal Production (1943) [video]

It's notable how many of these steps are there just to deal with defects found in the natural Brazilian quartz that the process starts with. In a 41 minute video, it takes nearly until minute 18 before they're done identifying crystal sections that are unusable just due to imperfections (mostly twinning) in the original source material.

After the war, hydrothermally grown synthetic quartz crystals came to replace Brazilian quartz. The move to synthetic crystals mitigated the strategic dependency on quartz coming from specific distant geography. It also permitted cheap, small fragments of any old quartz to be grown into high-quality crystals. The synthetic crystals were free of twinning defects as-grown, eliminating some inspection/removal steps. Their size could be made more uniform than natural quartz, which permitted a higher degree of automation in processing.

It's notable how large the crystals are.

Quartz crystals work pretty much independent of size. Since it's a hard-to-obtain raw ingredient, and requires quite a lot of preprocessing before it's useful, I'm surprised that the final crystal size used in the radios isn't 1mmx1mmx0.5mm or smaller, even with 1940's technology.

I love these old-timey videos.