  We perform a series of experiments to measure Lagrangian trajectories of
settling and rising particles as they traverse a density interface of thickness
$h$ using an index-matched water-salt-ethanol solution. The experiments confirm
the substantial deceleration that particles experience as a result of the
additional force exerted on the particle due to the sudden change in density.
This stratification force is calculated from the measurement data for all
particle trajectories. In the absence of suitable parameterizations in the
literature, a simple phenomenological model is developed which relies on
parameterizations of the effective wake volume and recovery time scale. The
model accurately predicts the particle trajectories obtained in our experiments
and those of \cite{Fernando1999}. Furthermore, the model demonstrates that the
problem depends on four key parameters, namely the entrance Reynolds number
$Re_1$, entrance Froude number $Fr$, particle to fluid density ratio
$\rho_p/\rho_f$, and relative interface thickness $h/a$.
