Electrotyping was also used to produce entire printing plates directly from the formes composed from movable type and illustrations. In this application, electrotyping was a higher quality but more costly alternative to stereotyping, which involved casting of type metal into a mold prepared from the forme. Stereotyping had been invented around 1725, and was already well-established when electrotyping was invented in 1838. Both methods yielded plates that could be preserved in case of future needs, for example in the printing of novels and other books of unpredictable popularity. The movable type used to compose the original forme could then be re-used. Both methods could be used to prepared curved plates for rotary presses, which were used for the longest print runs. The widespread adoption of electrotyping for this use occurred after mechanical electrical generators (dynamos) became commonly available around 1872. These generators supplanted the whole rooms of chemical batteries (Smee cells) that were previously used to provide electricity for electrotyping. Batteries did not have the electrical capacity needed to rapidly deposit the electrotype (or "electro"). The advent of plating dynamos sped up electrotyping twenty times or more, so that an electrotype printing plate could be deposited in less than two hours. In addition, the chemical batteries gave off toxic fumes that had required their isolation in separate rooms.