When a thin film of initially hydrated gelatin is allowed to dry from the surface, superficial changes in the structure
of the material affect the local mechanical properties of the drying region. If the film is simultaneously subjected to
large strain deformation (above 20%), a periodic pattern of wrinkles appears on the surface of the gelatin along the
length of the sample in the direction of the applied force. These wrinkles are uniformly distributed on the surface of
the gelatin with a wavelength that is much smaller than the sample thickness, which changes with sample composition,
aging time, and deformation rate. We investigate these patterns via in situ environmentalscanning electron microscopy
(ESEM) and provide a theory for their origin.