pigment composition

A pigment’s physical properties play a vital role in it’s performance. Particle size, particle shape and distribution, and refractivity all affect the color, opacity/transparency, finish and durability.

It may seem inconsequential but pigment chemistry helps us understand how particular pigments degrade or react to environmental influences. It can also influence and make our pigment choices more intentional and improve the quality of our paintings.

When I started doing conservation work with pigments on Indigenous artifacts I needed to identify each pigment elementally which provided a wealth of information about the object such as time period it was made, place of origin, and other details. The elemental analysis is a good way of matching sibling artifacts and sometimes, the source of the pigment. Through atomic weights and trace elements I have been able to match sibling artifacts and in a couple of cases, the source of the pigments.

This kind of information is vital in learning more about objects and cultures of the past, but doesn't necessarily help when you're looking your paint palette. What you gain as an artist from this kind of analysis is a deeper understanding of the nature of the material you're using.

The graphs below are two examples of the same pigment from different sources. Each sample has its own elemental signature that includes all the elements and atomic weights that are unique from all other sources. For example, one sample contained strontium which is not commonly found with Vivianite in nature. Using that signature I was able to match the sample to a specific Vivianite deposit which I added to the documentation the museum had for that artifact.

The top section of each data sheet below shows the amounts of each element present in a sample while the chart below those gives us the atomic weights. Both of these are samples of Vivianite from different sources (different continents!) and you can clearly see how they have the same main elements--iron and phosphorus, but the second one also contains aluminum, chlorine, sodium and other elements.

Each inorganic pigment has a unique elemental composition. For example, red ochre, for which the scientific name is iron oxide, has a simple composition of the elements iron (ferrum) and oxygen. As you can see from the diagram above, there are 3 atoms of oxygen to 2 atoms of iron for every iron oxide molecule.

Other inorganic pigments, whether they are natural or synthetic, have their own chemical formula that shows from which elements, and how many atoms of each element, make up that pigment.

The Periodic Table above isn't intended to make you go cross-eyed and get a headache; it's an important tool to have when you want to understand your pigments better. Now, I cried everyday after chemistry (the whole 3 weeks of college chem I took before dropping out in frustration and dismay!), and swore I couldn't think of a single good reason I should learn any of this. Well, that came back to bite me when I started working with pigments and analyzing them to understand their natures better. This isn't to say I know anything about chemistry, but I've found that knowing vermilion is derived from mercury, I at least know not to lick it.

But also knowing that iron oxides and umbers, while both having iron in their makeup, umbers also have manganese which makes the colors cooler, slightly more green and ranging into darker hues. It's the amount of manganese that determines the shade and depth of umber color. Compare umbers to siennas and we find siennas carry more iron oxide and less manganese making the colors warmer and lighter but ranging from yellow to reddish brown.

For many, the amount of manganese in a pigment will not affect your choices of what color to paint something,

I have come to rely on my periodic table so much, I have one hanging over my desk. I refer to it often when I want to delve into the "dna" of a pigment, see who it's related to, how it will behave, and where it'll play nicely.

So, if you're as curious and nosy as I am, you'll come to regard your periodic table as a valuable tool!

One of the simplest and most abundant mineral compounds is iron oxide. With only two elements, iron and oxygen, with two parts iron and three parts oxygen