(07-12-2025, 01:30 PM)Jorge_Stolfi wrote: You are not allowed to view links. Register or Login to view.On vellum, neither ink nor paint can get into the material to any significant amount. There, iron-gall is not just better than lampblack, it is necessary in order to get writing that does not rub or wash off at the first challenge. It works by binding chemically to the proteins in the vellum, and then becoming an insoluble 3D polymer of tannin and iron. Other color pigments need a good binder that can glue them to the vellum; but all common binders decay, or are not water-resistant.
I'm not a chemist, but I can't understand it just from the common sense perspective. As it was said elsewhere the ink reacts chemically with the vellum. Obviously even if the ink is applied over the (water soluble) paint, it will seep through to the vellum and react with the vellum, creating a dark patch under the paint. So, the fact that the green paint appears over the charred vellum doesn't necessarily mean that it was applied later than the ink.
What is wrong with this reasoning and why do people use "over" the ink and "under" the paint here to infer the order of events?