Thus, in both of these N132D and in N49, we find that Fe-bearing dust grains are not fully destroyed until they reach the recombination zone of the shock. The detail of the grain destruction process were discussed in @Dopita16, where it was concluded that this type of depletion pattern supports the grain destruction model of @Seab83 and @Borkowski95.

\[Ni II\] diagnostics
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Since we also observe strong \[\]$\lambda 7378$, it is worth asking whether the Ni-containing grains suffer the same fate as the Fe-containing grains. The diagnostic plots for \[\]/H$\alpha$ are given in Figure \[fig11\]. We find a depletion factor of $\sim -0.4$, intermediate between the \[\] and \[\] results, but again consistent with a large fraction of dust grains being destroyed in the shock.

The highly ionised species of Fe
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To produce the highly ionised species of Fe; \[\]${\lambda 8235}$, \[\]${\lambda 6374}$ and \[\]${\lambda 5303}$ requires shock velocities $v_s \gtrsim 200$km/s. Indeed, the self-consistent radiative shock models do not produce strong \[\]${\lambda 6374}$ until $v_s \sim 250$km/s and \[\]${\lambda 5303}$ becomes bright only for $v_s > 350$km/s. The diagnostics of expansion velocity, velocity dispersion, and the spectral diagnostics presented above all point to shock velocities for typical clouds 