Visible light irradiation of an aqueous solution of sodium alginate and organometallic complex [(C₅H₅)Fe(toluene)]BF₄ transforms it into a rigid hydrogel due to crosslinking of the carboxylate groups by the iron ions. Irradiation of the same iron complex together with K₂S₂O₈ initiates the polymerization of acrylamide, which provides an efficient method for light-controlled one-step preparation of alginate-polyacrylamide double network hydrogels, which are capable of gluing wet glass with 100–200 kPa shear strength.