For a)materials
b)rejection rate as De bethune won t settle for second grade
c)hours of intervention by hand from a skilled artisan
d)small production
The dials on the DB 25 starry sky for example takes 4 or 5 different stages to obtain a blue like that from titanium...and the rejection is quite high.
If you inspect closely a guillochet from DB again you 'll find that its quite difficult to find a more exquisite one on the market.
Mo