You have surely noticed that pebble-stone colors get deeper and brighter when they are wet, and that this effect disappears as soon as they dry. What happens with encaustic colors is very similar to what happens when a porous object gets wet, or when painters varnish their paintings.
You may have wondered why encaustic colors are so lush? why wax-medium changes so much the appearance of some paper? If you are going to be busy with encaustic and mix media, you will have to get acquainted with the optical effects that make of encaustic such a wonderful experience.
A little bit of optics: Reflection & refraction
How light interacts with the microstructure of materials determines why the materials look they way they do.
We all know why objects show the color they show, but do you know why do translucent objects look the way they do?
Objects generally both reflect and refract light rays at the same time but in different proportions. Opaque objects reflect most of the light rays, translucent objects refract most of the the light rays. How light is reflected and how light is refracted determines the translucency grade of the material.
The way light is reflected depends very much of the surface of the object. Depending on how light reflects you get different types of surfaces: specular, glossy or diffuse.
Specular reflection is the mirror-like reflection from a surface, in which light from a single incoming direction is reflected into a single outgoing direction. This type of reflection happens when the surface is perfectly smooth. Reflections on still water or a polished metal are an examples of specular reflection.
When the surface is not perfectly smooth, rays are reflected in directions deviated from the ideal mirror direction. When the deviation cone is narrow the reflected light is highly concentrated and creates glares in specific areas, like glossy paper photo does for instance.
If the surface has an irregular structure, the light is scattered in all directions (lambertian surface) and we can perceive a diffuse reflection, like unpolished marble or wood.
Light travels in a straight line, but when a light ray passes from one medium into a second medium the light direction bends at the boundary, this bending effect is called refraction and is due to the different velocities at which light travels in each medium.
The relationship between the vacuum speed of light and the speed through a material can be expressed as a ratio called Refractive Index (RI). Depending on this Refractive Index the angle of tis bend according to the snell’s law.
RI 1 . sinα1 = RI2 . sinα2
(The higher the RI -> stronger the bending)
What the Snell law’s determines is that, when light travels from a higher refractive index medium to a lower refractive medium, part of the light is trapped within the layer of higher RI, and the ray cannot scape keeping bounding internally (a little like the greenhouse effect).The higher the Refractive index of a material, the higher the percentage of light that will be trapped in it. For instance 72 % of the incoming light will be trapped in a diamond, while 55 % will be trapped in a varnish.
This optical property of the materials with high RI is responsible for the “wet” effect (see graphic below) and is also the principle how the optical fiber works or LED lights. The metamaterials are new materials with either very high RI (for the time being the most extreme material has 38,6!) or RI bellow 0 (negative RI) that bend the light in the opposite direction meaning that if you coat an object with this material you can make it invisible (isn’t it incredible!) some links about it here and here.
Varnishes how they work
An unvarnished surface scatters a portion of the white light and the rest enters the paint layer where some colors are absorbed and the rest is reflected back out as colored light. We see both the scattered white light and the colored component.
When we varnish the surface, some of the white light is reflected as specular reflection (glare) and the rest enters the paint layer where, again, some colors are absorbed and the rest is reflected out as colored light, however there is no scattered component of the white light. The colors appear richer and more saturated.
And encaustic? Encaustic medium is not but a translucent varnish applied in different layers, each one of the layers reflects and refracts the incoming light creating a sense of depth and translucency similar to that of the human skin, scientifically is known as subsurface scattering, but I will write about it sometime in the future.