The invention of the camera changed music printing once again. Photolithography became a practical process to copy music. This method involved transferring a photo image to a stone or metal plate using chemicals and then treated to produce a printing surface.
The Halstan Process
The Halstan Process was another method of printing music. It was created by Harold (Hal) Smith and his brother Stanley (Stan) Smith. The music was written out in blue pencil about four times its original size. Black ink was used to outline the blue markings. A photo was then taken and reduced in size. The blue pencil markings did not appear on the photo. The proof was then used to duplicate the music.
For more on the Halstan Process, please see the video below.