Re: gum arabic
There is no comment here about the original watercolor image having changed color. It is just the inappropriate use of gum as a varnish that has failed. There are many examples of gum being used as a binder going back much further without failure. Generally the only concern with really old watercolor painting is the viability of the pigments used at the time.
2009/1/30 Loris Medici <firstname.lastname@example.org>
Maybe, but they're also talking about darkening (cracking is another