Hi everyone,

This may be a bit of hair splitting but I always appreciate knowing as much as I can about the things which interest me.

In this Wiki post http://en.wikipedia.org/wiki/Fresco
it states that pigments "sink" into the plaster. While there may be a semantic difference in regards to what sink is, it is not my understanding or experience with the technique of fresco. I know frescoes scratch to reveal the intonaco's white makeup. The post also mentions a "mezzo" technique which seems more familiar to me.

It is my understanding that the pigment particles in buon fresco technique accumulate at the surface of the plaster while the water passes through the plaster (like a very dense filter). Eventually these particles at the surface become locked in by crystals created when the plaster reacts with Carbon Dioxide, becoming calcium carbonate.

For clarity's sake, what does a fresco surface look like under the microscope? Are there images of this anywhere on the web (i can't seem to find them). Technically speaking, is the post on wiki correct?

Thanks!

You are absolutely correct.

Pigment does not "sink" into the plaster but rather stays on the surface while the crystal forms around it. this is also a reason why the painting must be done with very "thin" paints otherwise the pigment will not adhere (crystals will not properly form around pigment particles)and will dust of when dry.

it is practiced often a "true secco" sometimes refered to as mezzo that is not really advertized because it is easily passed as buon fresco to frersco-unsofisticated person. i this technique painting is done when the wall is already dry or in process of drying - a thick layer of lime paint is applied to the wall and painting is done with pigments mixed into the lime paint and with galazes of thin paints - you can esaily spot that when you cant find a giornata (painting day) joints and it apppears that the painting is done in one section. it is possible because in order to keep painting all you need is to keep the wall moist by wetting. This is very commonly practiced technique, the result is a little chalky and colors are not as deep as buon fresco. also the surface is not as "tight" (strong) as with buon fresco and the life of this painting is not as long due to that.

PS about wiki - that part "pigment sinking" is not accurate, but as you pointed out "sinking" is not a well defind term in this case.