Dear Aldo, That finish is called "Crackle". Popularized in the UK especially by Claud Butler's. Toni Merkens was very popular here in the UK. This was when anti German feeling was still very high, scars from the Great War and the rise of Hitler. Toni I think rode a Gold Rad. He also rode a Hetchin's and a Butler. This might even be a re-badged Claud as it has the distinctive Butler Crackle finish. Toni Merkens and Albert Richter were wonderful ambassadors for Germany in very difficult times. They were much loved and admired here. Yours fraternally Frank.
Frank Cohen Hoxton UK