Henderson - Casein, Catalin, & Celluloid
To the left we have what is believed to be a 1925 Henderson with hallmarked silver. The problem is that some of the silver is hallmarked 1925 and some is hallmarked later. Still, profiles tend to line up with Henderson pipes from the 1920's.

The Henderson bagpipe immediately below is from the mid to late 1960's. You can see that the profile has changed and that the beading and combing has changed. These were made during Greg Sharpe's tenure as shop foreman and were excellent bagpipes.
The instrument to the left is believed to be from 1936, which is consistent with what we know of Henderson bagpipes from that era. I do have pictures of an early silver and celluloid stamped Henderson however the pictures are too small and you can't really see the detail. I found that bagpipe with a badly repaired pin on the mid-section. Once repaired properly it turned out to be one of the best bagpipes in the band.
Casein allows us to date the bagpipe around WWI. It was abandoned when catalin became the imitation ivory material of choice. As you can see, mounts were sometimes made in two pieces. Casein picks up dirt and grime quite easily and frequently shows it. James Robertson has the best casein of all the makers. Although brittle, casein is favorite of mine.