  In drying coatings, the time span between the deposition of the wet film and
the formation of an uniform solid harbors a procession of complex phenomena
each of which carves the final properties of the dry paint film. Attaining a
better control of the drying process requires the availability of a tool that
allows monitoring the attending dynamics. The experimental access to the
dynamics underlying the drying process is challenging as paint films are often
opaque and the phenomena accompanying the drying process usually populate a
multitude of time and length scales. To circumvent these obstacles we deploy
Laser Speckle Imaging (LSI) as a technique that allow us to quantitatively
probe the internal dynamics of drying waterborne paints and unambiguously
determine a crucial handling parameter such as the open time. We develop a set
of scaling relations which accurately predict the behavior of the
experimentally determined open time as a function of a parameter set that
governs the drying process. Additionally, we harness the big temporal dynamic
range of LSI to monitor phenomena that inhabit the later stages of the drying
process. Remarkably, we not only capture the film formation time, the time
point in which phase inversion takes place, but also microscopically detect the
deformation of polymeric particles that precedes it.
