  This paper is dedicated to the solidification of a water drop impacting a
cold solid surface. In a first part, we establish a 1D solidification model,
derived from the Stefan problem, that aims at predicting the freezing dynamic
of a liquid on a cold substrate, taking into account the thermal properties of
this substrate. This model is then experimentally validated through a 1D
solidification setup, using different liquids and substrates. In a second part,
we show that during the actual drop spreading, a thin layer of ice develops
between the water and the substrate, and pins the contact line at its edge when
the drop reaches its maximal diameter. The liquid film then remains still on
its ice and keeps freezing. This configuration lasts until the contact line
eventually depins and the liquid film retracts on the ice. We measure and
interpret this crucial time of freezing during which the main ice layer is
built. Finally, we compare our 1D model prediction to the thickness of this ice
pancake and we find a very good agreement. This allows us to provide a general
expression for the frozen drop main thickness, using the drop impact and liquid
parameters.
