Here is a report on research for Da Vinci. It says he had been used half a human hair thickness glaze and paint layers , sometimes 30 layers , at his paintings.
Here is the question , is it possible to create a emulsion for portraits with exposable glaze dye layers in it ?

Here is the news report from aol :

It's one of the things about the "Mona Lisa" that's long baffled art historians and viewers alike -- how Leonardo da Vinci used rudimentary pigments in the year 1503 to create such subtle shadows and light on the mysterious woman's face.

And it's taken scientists more than 400 years to come up with technology to figure out how.

Now French researchers are using X-ray fluorescence spectroscopy, a noninvasive technique, to isolate and study each ultra-thin layer of paint and glaze da Vinci used on the "Mona Lisa" and six other paintings at Paris' Louvre Museum. Scientists from the Center for Research and Restoration of the Museums of France brought their high-tech machine into the museum while it was closed, and zeroed in on faces depicted in the paintings, which have a dreamy, hazy quality about them.

ESRF, V.A Sol / AP
Specialists from the Center for Research and Restoration of the Museums of France found that Leonardo da Vinci painted up to 30 layers of paint on his works to meet his standards of subtlety.
Da Vinci used a renaissance painting technique called "sfumato," mixing thin layers of pigment, glaze and oil intricately to yield the appearance of lifelike shadows and light. The technique is well known and has been employed by other artists over the years. But only now have scientists been able to analyze just how intricate da Vinci's layers are.

They believe da Vinci used up to 30 layers of paint on his works. But altogether they only add up to a thickness of less than 40 micrometers of paint -- about half the width of a human hair. Details were reported Friday by several news agencies.

The scientists were able to beam X-ray technology at the paintings without even removing them from the museum wall.

"This will help us to understand how da Vinci made his materials... the amount of oil that was mixed with pigments, the nature of the organic materials," senior scientist Philippe Walter told CNN. "It will help art historians."

The new analysis also shows that da Vinci was constantly trying out new mixes and methods. In the "Mona Lisa," he mixed manganese oxide with his paints, but in others he used copper, Walter also told The Associated Press. Da Vinci used glazes in some paintings but omitted them altogether in others, he added.

"We realize when glazed over, for instance on the 'Mona Lisa,' that he managed to place layers as thin as one or two micrometers, which means one or two thousandths of a millimeter," Walter told EuroNews. "By super-imposing the layers very progressively and slowly, he managed to create the effect he was seeking."

The research was published in Wednesday's issue of a chemistry journal, Angewandte Chemie International Edition. In addition to the 'Mona Lisa,' scientists also studied Leonardo's Virgin of the Rocks, Saint John the Baptist, Annunciation, Bacchus, Belle Ferronniere, Saint Anne and the Virgin and the Child, Agence France-Presse reported.

While this research solves one mystery about the "Mona Lisa," others persist, like who the enigmatic woman is, and why she holds that subtle half-smile. Many experts believe she's Lisa Gherardini, the wife of a prominent merchant from Florence. Da Vinci is believed to have started the painting in 1503, and worked on it for four years.

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Mustafa Umut Sarac