Instrument Development - from Kayla Nelson's wonderful hornhistory.com site.
Carl Geyer - a reminiscence by Tom Bacon
Early American Brass Makers, book by Robert Eliason
Horn Manufacturers - Erin Schmidt has compiled a page of many horn manufacturers that compares alloy, bore, and price (plus comments). Nice work!
Dissertation: McLaughlin, Brian James. “American Horn Making in the Twentieth Century.” D.M.A. Essay, University of Iowa, 1998.
Excellent video portrait of Engelbert Schmid (in German) about his career as a player and as an instrument maker, richly acoustically decorated with background horn ensemble music. 8' 34"
A Horn is Born - making a natural horn
First Steps in Making a Horn - a wonderful, if brief, Quicktime movie showing how the process of building a horn begins.
Horn Factory TourYamaha offers an online illustrated tour of the manufacturing process of horns. Factory Tour 2.
J. Meinlschmidt GmbH - Valvemaker to the stars...
Making a Vienna Horn - a YouTube video of Robert Engel making a Vienna horn
Constructing a Natural Horn - at Atelier Harlow in Tokyo [photos]
Natural Horn Businesses - Links to natural horn makers, etc., courtesy of Early Music Chicago.