[CR] Double-butted spokes?

Example: Production Builders:Frejus

To: C R List <classicrendezvous@bikelist.org>
From: Mark Buswell <mark@sisuhome.com>
Subject: [CR] Double-butted spokes?
Date: Fri, 2 Nov 2007 22:53:18 -0700

I'm building up a set of wheels for my 1981 Merckx and was wondering: When did double-butted spokes first come into common use?

Mark Buswell
San Francisco, CA