RE: What's happening here ?
** I concur with Mr. Marin although there ARE spots of "redish stuff".* When electrolysis occurs on bronze objects, a strut in this case, the usual material "lost" is tin, initially leaving the* surface richer in copper which oxidises to, in some cases to Copper (1) Oxide which is reddish in color.* Copper (2) Oxide is black.* The green sometimes seen on copper could be a copper sulphate or a copper carbonate compound.
** Further de-staninification will eventually destroy the fitting.
** Not saying the strut in the picture IS suffering from electrolysis-really can't tell.
** Golly, Chem 101 was eons ago...