Those Levenger erasers were Carolyn Gast's idea and were written up in
a recent Guild Newsletter. I am delighted that Gail found a similar
or identical one for less money.
Carolyn recommends the erasers for use with carbon dust, grinding
them and graphite separately, then applying the eraser dust alone and
with varying combinations of graphite to create soft highlights. This
is a technique she used to use with "soap" erasers, which seem not to
be available any longer.
The first time I tried this Levenger eraser/graphite technique I
liked it, but later did not. So it is all individual. I can create
soft highlights with chamois and then a pointed eraser for the
central, whitest highlights. However, no one can create a more
beautiful carbon dust drawing than Carolyn (with the exception of
Gerald Hodge and Max Broedel), so when she speaks I listen.