  There has been much discussion recently regarding entanglement
transformations in terms of local filtering operations and whether the optimal
entanglement for an arbitrary two-qubit state could be realised. We introduce
an experimentally realisable scheme for manipulating the entanglement of an
arbitrary state of two polarisation entangled qubits. This scheme is then used
to provide some perspective to the mathematical concepts inherent in this field
with respect to a laboratory environment. Specifically, we look at how to
extract enhanced entanglement from systems with a fixed rank and in the case
where the rank of the density operator for the state can be reduced, show how
the state can be made arbitrarily close to a maximally entangled pure state. In
this context we also discuss bounds on entanglement in mixed states.
