  We report shear viscosity of heavy water supercooled $33\,\mathrm{K}$ below
its melting point, revealing a 15-fold increase compared to room temperature.
We also confirm our previous data for the viscosity of supercooled light water,
and reach a better accuracy. Our measurements, based on the spontaneous
Brownian motion of $350\,\mathrm{nm}$ spheres, disagree at the lowest
temperature with the only other available data, based on Poiseuille flow in a
narrow capillary, which may have been biased by electro-osmotic effects. The
viscosity ratio between the two isotopes reaches 2.2 at the lowest temperature.
A companion Letter [F. Caupin, P. Ragueneau, and B. Issenmann,
arXiv:2112.09010] discusses this giant dynamic isotopic effect. Here we provide
a detailed description of the experiment and its analysis. We review the
literature data about dynamic properties of water (viscosity, self-diffusion
coefficient, and rotational correlation time), discuss their temperature
dependence and compare their decoupling in the two isotopes.
