Photo paper manufacturers, although sometimes close connected with picture postcard trade and research (eg the Mimosa and E.A.S. / Ross / Rotophot business relationship), belong more to general photographic history.
An article on Mimosa AG, Dresden is found in TPA 26.
A photo of the huge Rotophot Berlin bromide photo printing (‘by the mile’) plant will be illustrated in TPA 27.
Inquiries on this topic welcome.