  A drop impacting a solid surface with sufficient velocity will emit many
small droplets creating a splash. However, splashing is completely suppressed
if the surrounding gas pressure is lowered. The mechanism by which the gas
affects splashing remains unknown. We use high-speed interference imaging to
measure the air beneath all regions of a spreading viscous drop as well as
optical absorption to measure the drop thickness. Although an initial air
bubble is created on impact, no significant air layer persists until the time a
splash is created. This suggests that splashing in our experimentally
accessible range of viscosities is initiated at the edge of the drop as it
encroaches into the surrounding gas.
