Masaharu (政春) was the eldest son of Tamagawa Yoshinaga (玉川吉長, 1747-1804) from Mito. Masaharu was the 3rd generation from Tamagawa School founder: Tsugutoshi (承寿). Initially his name was Jūgorō (重五郎) and later Yūzō (勇蔵). During his artistic period he used followed family names: Ishiguro (石黒), Tamagawa (玉川), Shōji (庄司), and Onuki (小貫). Masaharu firstly studied under his father Tamagawa Yoshonaga and then under Tamagawa Yoshihisa (玉川美久, 1st generation of Tamagawa School). Later he studied under Shōji Yoshimasa (庄司美政) and then Masaharu moved to Edo to continue his education under Ishiguro Masatsune (石黒政常). He received the «masa» kanji from Masatsune’s name. Masaharu lived in Mito and Edo. He signed as Ishiguro Masaharu, Masaharu and Yoshinari (supposedly) using also the followed nicknames as well: Genshōsai (玄松斎), Shōsai (松斎), Kensendō (堅鐫斎).
Masaharu’s signature example (The Kinko Meikan by Masumoto and Kokubo, Tokyo 1974, p.453).
There is a theory that the second Masaharu who studied in Mito under Tamagawa Yoshinari (玉川義成) and later under Ishiguro Masatsune. He belonged to Onuki family and his nickname was Jukakusai (寿鶴斎). But it is most likely that different entires in old manuscripts describes the same kinko artist who used many family names during his artistic period.
In photos: the Tokubetsu Hozon tsuba signed Genshōsai Masaharu kaō (玄松斎政春).