Date not known. Theodor Maas is a still running company dealing with tea. (Website)
Currently no more Information are available about this issues.
- Are there more values and colours available ?
- Why did the “Cinderella” have a value, some also overprinted ?
Any Comments are welcome, contact email@example.com to send scans of your Maas stamps, too. Are covers, postcard or Newspaper known with this stamp ?