The long strip of holographic film was placed between the loose glass sheet and the front of the camera, and the entire camera box was then almost filled with Johnson's Baby Oil. This unusual element to the high tech array of equipment and processes came about after the exhaustive testing of the refractive index of countless varieties of commercially available oils, and to the surprise of the holographers concerned, none could surpass the efficacy of this product. The function of the oil inside the camera was to act as an agent to cause the camera to flatten the film between the two glass surfaces. As the oil slowly seeped out between the film's surface and the two glass sheets the natural viscosity of the oil maintained an ultra-thin but cohesive layer that had the effect of gradually pulling the two glass sheets together with a level of force sufficient to flatten the film to within the tolerance level that allowed a consistent interference pattern to be recorded on the H1 master.