David Glen began making bagpipes with his father, Alexander Glen. The picture below-left was sent to me by David Glen of London.  It had belonged to his grandfather, George Glen (b July 1, 1889).  His great grandfather was also *George Glen (b October 1, 1863) and his great, great grandfather was Alexander Glen (b 1801).  This picture is of Alexander Glen with a young David Glen ca 1873.  
He opened David Glen Bagpipe Maker in 1873. His sons Alexander (Sandy) and David Jr. continued the business as David Glen and Sons until David Jr retired from the business in 1949. The remaining stock was sold to J & R Glen at that time.  If you're interested in the Glen family there is an excellent book entitled The Glen Descendants of George Glen (1724 - 1804) ISBN 0-9695019-0-0.
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When you find a David Glen or David Glen and Sons bagpipe, expect to find impeccable styling, beading and combing, and finishing.  Without any doubt, David Glen bagpipes represent the very best in craftsmanship and in design. 
The "classic" David Glen bagpipe is likely to be made of cocus wood with wood mounts as shown in these pictures.  The cord beads are delicate and nicely contoured.  Stocks are straight-sided however generally a bit bigger than those made by J&R Glen.  The name is sometimes found in the flat just beneath the ferrule on the bass stock.  If there, it will likely be very faint.
David also worked with ivory and you may or may not encounter projecting mounts with a cut-bead.  Regardless, the workmanship will be outstanding.
More pictures of David Glen bagpipes
David Glen