Transparent magnetic glass-ceramics were produced by infiltrating nano-porous glass with nitrate salts and firing. The resultant glass-ceramics contained spinel ferrite nanocrystals; that exhibited ferromagnetic and superparamagnetic behavior depending on composition and firing temperature. Transparency in the near infrared was obtained when oxidizing conditions were used to prevent Fe (2+) formation, while the porous matrix ensured nano-sized crystallites; to limit scattering losses. MnFe2O4 glassceramics treated at 1000 degrees C offered the best combination of magnetic and optical properties with a saturation magnetization of 5.6 emu/g, a Verdet constant of 16.5 degrees/cm, and losses below 3 dB/mm at 1550 nm.