This will solve the problem and you can
overpaint Zinsser B-I-N within 30 minutes of application.
Here's just one of his scads of instrumental tips: "The key is to stop before you
overpaint!"
It should also brighten them up a bit, but if the paint has yellowed then you will need to
overpaint them to get a pure white finish.
You can either go for a direct–to–uPVC topcoat paint or, my preference, a uPVC primer, which allows you to
overpaint with any finishing top coat paint of your choice.
"The original paint layers were further obscured by large areas of
overpaint from past restorations, which were obvious even under the heavy layers of surface dirt and varnishes.
In the lab, our intern, Sayeh khajeian, systematically identified and treated discrete areas of damage obscured by copious amounts of
overpaint and the soot that had likely come from a domestic furnace or fireplace and had accumulated over many years.
The restorers also encountered several sections of
overpaint and a second canvas lining the original, thus slightly reducing the image at its lower edge.
According to a person familiar with the painting's history, da Vinci's hand was confirmed after the removal of layers of discoloured varnish and
overpaint applied by earlier restoration attempts.
The students reinforced the structural condition of the murals and improved their overall aesthetic condition by removing surface grime and torn mending and by cleaning and removing discolored and incorrect
overpaint. Next spring and summer, the museum and WUDPAC will host another summer work project to complete the second phase of the restoration.
Layers of
overpaint had been added in the later part of the 17th century, obscuring its provenance.