There was learned opinion that probably all (but certainly most) 'tortoiseshell' on concertinas was man made imitation, thus side-stepping the problem.
I don't remember anyone discussing the artificial version any more than that. But I think tortoiseshell finishes look superb and it occurred to me to wonder if any of our current makers had ever looked into offering tortoiseshell on their instruments?
Edited to add: OF COURSE using the artificial stuff...
Edited by Dirge, 18 March 2012 - 01:32 PM.