Letter Writing Set

All I know is the obvious - it's a letter writing set.

On the fountain pen, I can see "Rester 556" but no other markings appear on any other item OR the box.

I have found three other sets online, which indicate the 1920's and one indicates it's made of vulcanite and brass.

Does anyone know just by the picture if the time period is correct and possibly what this is made out of?

Thank you for looking!