the answers are a lot easier than you imagine.
more pigment (we have to be clear as to which solids we are discussing, because the
binder is considered a solid in a dried paint film) is added to paint, the PVC is
increased. If more binder is added the PVC is lowered because the
percentage of pigment in relation to the binder decreases. As I wrote
in my previous answer, solvents and diluents are not part of the calculation of PVC. Egg tempera paint is never at the CPVC of the
pigment or pigments in the paint, because egg yolk does not envelop
pigment particles in the dried paint film. If you examine egg tempera
paint films at high magnification the egg yolk would appear as tiny glue bridges connecting pigment particles. As a consequence egg tempera paint is a
naturally high PVC system.
Paint at its CPVC theoretically does not contain voids, because pigment particles
are enveloped by the binder and because of pigment packing interstices between pigments are
the smallest possible, so that particles are nearly in contact within one another except for a thin film of binder surrounding each particle.
Your understanding is correct, but when painters prepare egg tempera
paint they often add additional water so I included this water content which may
comprise 70% more or less of the liquid vehicle (binder and solvent) added to pigment. The percentage is not, of course, an absolute number because it
depends on how the paint is prepared.
As water in egg tempera paint evaporates the non-volatile portions of egg yolk adhere to pigment particles, forming air voids throughout the paint
5. The absorption of other binders, mostly alkyds, have been studied to better understand how these impact formulations and the calculations
of PVC and CPVC. I do not believe there is any practical benefit to knowing the absorption of egg yolk, since egg tempera is a high
Adding more pigment to paint (increasing PVC) does not change the
CPVC (that's a fixed value based on the amount of binder that completely envelops pigment particles with the densest pigment
packing), Changing the PVC by increasing it above the CPVC changes paint film properties, such as increasing permeability (making it more susceptible to solvents and water vapor),
decreasing tensile strength, and reducing gloss. Adhesion may also be
affected because there is less binder to wet the substrate, decreasing
the total surface area of the paint in contact with the support.
Paint that is less flexible is typically more susceptible to
cracking. Air voids increases the potential for diffusion of
oxygen and water vapor through the paint which is why it is more susceptible to fluctuations
in relative humidity. In addition, high PVC films (>CPVC), such as egg
tempera, are not good candidates for varnishing, because varnish is
absorbed into the paint film, thereby becoming part of the painting
and is very dfficult if not impossible to remove. To some degree paint films with high PVC
are also susceptible to abrasion, but this is also dependent upon the
type of pigments in the paint film.
to the high PVC nature of egg tempera it is more brittle compared to oil paint and more
susceptible to changes in the environment. For this reason it performs best when applied to
rigid supports. Varnishing egg tempera paintings is more complex compared to varnishing oil paintings; applying an isolating coating first to tempera paint film should be followed by a final protective coating that can later be removed.
Paints can be ranked in terms of their properties, such as tensile
strength, but that is only one aspect of the complete picture, and is
perhaps not entirely useful, since a painting is a composite
structure where the support, preparatory, pictorial and protective
layers interact with each another as one object (that is a zen-like statement
but it fits well the physical nature of paintings).