  R Coronae Borealis stars (RCBs) are cool supergiants that display
non-periodic deep dips in brightness. Recently, a group of `Hot RCB stars` has
been discovered to be fast evolving across the HR diagram, as these stars leave
the RCB region, with brightness changes at the rate of $\sim$1 mag/century.
Perhaps cool RCB stars can also be seen evolving, either increasing in
temperature as they evolve to become Hot RCB stars, or perhaps increasing in
luminosity as the stars arrive at the RCB region. To seek these changes, the
only possible method is to extract archival data going back more than a
century, looking for the brightness changes associated with the evolution. I
have measured and extracted 323,464 magnitudes (mostly from the Harvard plates
and from the AAVSO) for ten cool RCB stars, all with over a century for the
light curves, all consistently calibrated to a modern magnitude system. For
times away from any dips, these light curves are flat to within the typical
uncertainty of $\pm$0.10 mag/century. That is, I see no significant evolution.
I also have collected a large database of light curve dips and their
properties. From this, the light curves for all the well-observed isolated dips
have the same shape, featuring a flat slope for the few days immediately after
the minima. Further, I derive a general model for the shape of the light curve
for all isolated RCB dips, with a simple equation accurately describing the
observed recovery to maximum light.
