A simple methode to make slits or diffraction grating by hand was developed. The first, coat plane glass surface with a few drops of drawing ink, Next, make a micrometer screw move up and down the glass in a vertical plane to keep the spacing of rulings constant. And then, single, double or more number of slits are made by ruling fine grooves on the drawing ink thin film with a safety razor or a snap-off cutter brade on a horizontal plane bed.
A high quality grating which has 100 lines per mm is made simply in several minutes by students in the classroom.