The Science of Art: An Exploration of Paint and Color Theory

[Al Capwn]

I don't have a blog, and I am not veteran or post enough content to justify making one - so while these musings may be better served in that format, I will leave it here for anyone who is interested to view and chime in. It just so happens that my best friend happens to work at Rustoleum as a colorist; so lately I have been picking his brain since he has an extensive knowledge about pigments, paint make up, and the chemical intricacies therein.

 

As I have delved further and further into the hobby, I have been looking more into the deep subjects of color theory and how paint is made/composed. After reading James Gurney's Color and Light, as well as Michael Wilcox's Blue & Yellow Don't Make Green, I was really intrigued about what exactly paint is and how exactly color interactions work. Now I am guilty as the next person in owning WAY too many paints - not to say anything about minis!

 

While color mixing may seem irrelevant to some, understanding how paints function can help even those of us who own a complete gamut of convenience mixed colors. This post is about exploring more of the technical and "scientific" aspects of paint and color theory to hopefully assist others in understanding the what and why of paint.

 

Rethinking Paint Colors - Subtractive Color:

Up until recently, I have always viewed the primary colors as Yellow, Red and Blue, and with those you can mix secondary colors; Green, Orange, and Purple. While this is technically true after a fashion, the difficulty lies with pigments themselves. Pigments do not actually *contain* color. Instead, they absorb most of the light spectrum *except* a specific wavelength of color. As Michael Wilcox states, "Of all the pigments available to the painter, none can be described as pure in hue. There is simply no such thing as a pure red, yellow or blue paint." That means chemically, there isn't a paint pigment out there that returns a pure Red - unlike in say digital art where a specifically purely calibrated hue can be made, paint is limited by the properties of the physical pigments themselves.

 

As Michael Wilcox theorizes with a colour bias wheel (bottom-right), primary pigments almost certainly lean towards secondaries. This follows the concept of the Munsell Wheel (bottom-left). You may have heard of a split-complimentary color palette, and this is the reason why. Artistically, these have been described as "Warm" and "Cool" versions of the primaries, but scientifically, they are colors that absorb or reflect more of a particular wavelength. There are Violet-Reds (Cool Reds, often called "Crimson") and Orange-Reds (or Warm Reds, that lean more towards Orange), Violet-Blues and Green-Blues, and Orange-Yellows and Green-Yellows.

 

 

One the concepts to understand when mixing paints is that you are not creating a color, but rather you are effectively destroying colors and what remains is what is returned to the eye. Referencing the above color bias wheel, if you were to mix a Violet-Blue and a Violet-Red together, both containing pigment(s) that return a great deal of Violet wavelength, the little remaining Blue/Orange and Red/Green wavelengths in each pigment would cancel each other out, leaving the Violet behind.  This would yield a more saturated or more pure hue of Violet. Conversely, mixing a Green-Blue and a Orange-Red ("Warm" Red) would be a very desaturated Violet, with more of a gray tone.

 

Keep in mind that this doesn't make a color "bad"; desatured tones by including more complimentary colors is a very useful tool! In fact, for making shadows, using a great deal of complimentary colors to desaturate is a great technique. The problem is when these colors come about unexpectedly; after all, you can have a very "intense" Red and a very "intense" Blue, but mixing them may not produce a very intense Violet if they are "moving away" from each other.

 

Now that is all being said, it is time to forget it...sort of. RGB is based upon the concept of Additive Mixing, or how colored light interacts. With additive mixing, fully saturated Red/Green/Blue light will produce White light. However, in paint pigments, it should be pretty obvious that mixing pigment primaries of Red/Yellow (or Green)/Blue together will not yield White. This is due to Subtractive Mixing, where pigments effectively destroy each other ala Thunderdome in Mad Max, and only the survivors reflect light back.

 

A more modern approach to color theory and pigments is CMYK or Cyan, Magenta, Yellow and "Key" (or commonly known, Black). Adding these colors into the standard primaries gives us the "Yurmby" wheel. If you have looked at a color printer, for example, the colors used are NOT Blue/Red/Yellow, but rather Cyan/Magenta/Yellow. This is because due to the subtractive nature of pigment/ink mixing. These colors present a larger printable gamut (i.e. range) of color; for example, without White, it is difficult to produce a Pink tone with Red vs Magenta. A thin Magenta will read more Pink than a thin Red.

 

Printers do not use White ink and instead leverage the paper for white, effectively printers are printing in an underpainting style. However, we as artists DO use White pigments and this makes things a bit more complicated as we do work with Tints (White) and Shades (Black).

 

 

Like most science, the direct answer regarding an accurate color wheel is: it is complicated. For observable light, there is a bit more consistency and repeatability. However, when working with "tiny wavelength absorbing/reflecting mirrors" of pigments, things become a bit more complex. Additionally, there are other aspects that that go beyond the basics, such as the effect of specular and perception of color. It gets really heady when you start dipping into Kubelka-Monk Theory and K/S.

 

Paint Composition:

Most paint is made up of 3 parts:

Pigment - particles that absorb and reflect certain wavelengths of light.

Binder - The 'medium' or 'glue' which holds the pigment in suspension and forms a film. For acrylic paint, this is the actual acrylic part.

Solvent - The liquid that allows paint to be viscous; as it dries, it allows the binder and pigment to harden forming the film. For acrylic paint, the solvent is water.

 

Adjusting the ratios of these can have some interesting, and sometimes disastrous effects in terms of the stability of the paint. For example, introducing too much solvent, and the binder and pigment lattice structure can break apart. This can cause "coffee staining" or splotchy spots where the bonds pull apart, leaving areas without a film at all.

 

The pigments in paint are held in a suspension. Like hot chocolate mix, there are tiny particles that are suspended in a liquid. Given enough time or evaporation, the liquid will leave these granules behind. If you have ever mixed a packet of Swiss Miss cocoa, you know that the mix can settle at the bottom - and that attempting to add dry powder to a liquid is more difficult than adding a liquid to a dry powder. This is another reason why mixing your paints is important because it is easy for the heavier pigments to tend to settle out of the binder/solvent solution.

 

Speaking of solutions, that is the main difference between paints and inks. Inks, specifically alcohol inks that use dyes, are a solution. The staining dye actually becomes homogeneous with the liquid. Just like dissolving sugar or extracting coffee/tea, there isn't any particulates that separate out. However, most dyes are not lightfast - a property that will be discussed in more detail further. Acrylic inks that use pigments are not "true" inks insomuch as they are composed just like an acrylic paint. The difference being the smaller size of the pigments and the viscosity of the binder/solvent being much thinner.

 

Paint Additives

Outside of the 3 main components for paint composition, there are also some optional additives that some manufacturer's include in their paint. These can be things such as:

• Extenders/retarders, which delay the setup of the paint film, allowing for more mixing to occur before drying.
• Thinners, which dilute the pigment to binder ratio, usually increasing translucency and viscosity - commonly this is done with water for acrylic paints.
• Flow Aid, which reduces the surface tension of paint, allowing it to flow more easily and level - Reaper is known for adding a bit of flow aid into their formulation.
• Opacifiers, which increase the opacity of a paint - usually some type of calcium or bicarbonate.
• Matting agents, which reduces the glossiness of acrylic medium.
• Fillers, which are commonly used in student or inexpensive paints to reduce cost and add mass without adding more pigment.

 

You can add some of these additives yourself to your favorite brand of paint to adjust the handling qualities. The most commonly added is solvent/thinner in the form of water to "thin your paints" to reduce the viscosity and lower the overall density of the paint, building up multiple thinner layers of paint films in a "layering" fashion.

Edited March 29, 2020 by Al Capwn

[Al Capwn]

All About Pigments

 

So we have talked a bit about the color wheel, color mixing, and paint composition. We also have talked about pigments as they are particulates that absorb certain wavelengths and reflect another set of wavelengths.  As light enters paint, it is scattered all over. In a single pigment paint, this means that it will return back to the eye with the dominant wavelength that the pigment is "calibrated" for. Other wavelengths may be returned as well, but they will not be as strong as a certain frequency band of light.

 

 

When mixing pigments, as the light is scattered, it will hit different pigments. Because light is being scattered, some of the wavelengths that "should be" returned to the eye, bounce to another pigment particle and wavelengths are absorbed/reflected again.

 

Important Qualities for the Artist

When talking about pigments, there are a few qualities that we as artists are concerned with:

 

• Opacity: How much does this pigment cover a surface?
• Lightfastness: Will this pigment degrade with extended exposure to light?
• Tinting Strength: How "strong" or how much will this pigment affect another pigment?
• Finish: Matte or Glossy?
• Toxicity: How safe is this?
• Pigment Size: How large/small are the pigment particles?

 

There is a massive database out there called the Color Index which lists a vast array of pigments, and their properties. The best website I have found that covers the properties of these pigments is over at Artiscreation. Artist acrylic paints, such as Winsor & Newton and Golden (and notably Kimera Kolors specifically in the miniature painting line), list the exact pigment(s) used in the formulation of their paint. They use the Color Index (CI) and will also often list the opacity, lightfast rating, finish, tinting strength, and toxicity. Pigment size I have not seen ever declared, but this can be commonly seen in the difference between inexpensive craft paints which are more coarsely ground and contain more fillers, than with more expensive artist-grade paints.

 

 

 

Some pigments are naturally opaque in nature, such as Titanium White (PW6) and some other pigments tend to be very transparent, such as what tends to be the case with several Yellows (PY3) and Reds (PR112/PR122).

 

An unfortunate flaw in our hobby is that many paint manufacturer's do not list the pigment(s) used in their paint formulations. This means that it is really difficult to know exactly what pigment is being used and fully understand the properties therein. However, given the commercial popularity of many pigments, there can be a few assumptions made that many popular pigments are used even in the hobby paint realm. The downside is that some pigments are not lightfast, also called fugitive, which means they can rapidly lose their intensity over time with exposure to light. A common example of fugitive paints are typically Fluorescent paints, which may have optical enhancers, that will lose vibrancy with too much exposure to light.

 

This is something that I hope changes in the future within our hobby, listing the pigment CIs on the paint. I know most folks won't care, but for the few that do, they will be able to be rest assured that the pigment being used is of a high quality and provides the properties they are looking for.

Edited March 29, 2020 by Al Capwn

[Heisler]

It’s unlikely that we will see manufacturers list the pigments on their paints,  it would be considered proprietary information. Most of your information has been well discussed over the years on this forum. Thank you for bringing it together. Anne, developer of the current Reaper paint line, is a color genius! I have watched her break down another manufacturer’s color to its pigments in minutes.