The name Octave Viola is listed only by Audsley, who says: An open metal labial stop, of 4 ft. pitch, the tone of which is intended to imitate that of the orchestral Viola. An example exists in the Swell of the Willis Organ in St. George's Hall, Liverpool. Another, labelled Viola, 4-ft., exists in the Great of the same instrument, where it serves as the Octave to the Violoncello, 8 ft. Neither stop is highly imitative. . . . The imitative stop is more appropriately named Violetta. Adlung describes Violet as a 4' Viola or Viole (see Octave Viole).
Osiris contains seven examples of Octave Viola, all at 4' pitch. No examples are known of Violet, except for Adlung's cryptic reference to �Kindelbruck and Greussen�.