  We show an experimental evidence of the domination of absorption over
scattering in absorbance spectra of detonation nanodiamonds. We perform the
absorbance measurements on the UV-Vis spectrophotometer equipped with
integrating sphere and compare them with conventional absorbance spectra.
Additionally, we measure the scattering light intensity at the cuvette side
wall (scattering at 90 degrees angle). The obtained experimental data were
interpreted using the simulations of photon random walk in turbid media and
Kubelka-Munk approach. The scattering cross sections and indicatrices were
obtained by Mie theory.
  We discover that despite being very close to $\lambda^{-4}$ power law (like
Rayleigh scattering) the light extinction by the primary 4 nm diamond
crystallites is due to absorption only and scattering can be neglected. That is
the reason why previously absorption and scattering contributions were
confused. The scattering is governed only by the agglomerates of 100 nm and
larger in size remaining in the hydrosols and their fraction can be effectively
controlled by centrifugation. Only Mie theory reproduces correctly the close to
$\lambda^{-2}$ scattering by the agglomerates accounting for the weird
interplay between their size, fractal dimension, and dielectric properties.
Finally, using the obtained absorbance spectra we estimate the fraction of non
diamond phase in nanodiamonds and their agglomerates.
