Making the BW400CN into redscale film created the purplish tint in the photos. The reason you can do this with Kodak BW400CN film is because it is black and white film the is developed in color chemicals instead of black and white photo chemicals. If you want to try this technique just know that you will need more light coming through the camera, and go here to find out how to make a redscale film.
"With this roll of film I also attempted some double exposures with my Pentax K1000. I have owned this camera since high school and I have never once tried to take two pictures on one frame. This camera is not made to function in this way so I had to fuss with it to get it to work. What I did was take the first exposure, then instead of advancing the film I had to hold in the rewind button on the bottom of the camera and at the same time advance the film lever completely. Then I was able to take a second exposure. It did work, but with only two hands it was hard to hold in the rewind button and advance the film totally, so sometimes it only made it halfway around!" says Nicole Gelinas.