Oil painting cleaned with onion

A friend inherited an oil painting, approximately 100 years old, by
a well know artist from Denmark. It was very blackened from hanging
for all its years over a fireplace. The new owner was told that to
clean it, he should slice a Spanish onion in half and rub over the
painting, repeating with fresh onion until cleaned. This he did.
What an exquisite painting revealed. I recently found out how it was
cleaned approximately 2 years ago.  The onion was not washed off and
no other treatment was given.

I'm afraid for the future of this work. Please give suggestions for
preserving and opinions on any damage done to this work or damage it
will sustain in the future if left in it's present condition. Thank
you,

Carol Wickenhiser-Schaudt

                                  ***
                  Conservation DistList Instance 9:60
                   Distributed: Monday, March 4, 1996
                        Message Id: cdl-9-60-025
                                  ***