Glass Blowing: How to Marver and Cap - as part of the expert series by GeoBeats. By marver, just by turning left and right on the marver and shape the glass, then I can introduce air. It is called capping and blowing Where I have my right thumb on the back of the pipe so the air comes in when I am not blowing. That is because I put my right thumb here after I force the air in. I go like this. I trap air and the air is forced up into the glass, and it expands as it heats up.
