Summary: The art materials industry provides a wealth of color choices, but sometimes a gap is found in if a 12-step color wheel is used to map color choices. Further, can the color purple truly have an unbiased hue that is neutral and thus is neither a warm purple nor a cool purple? Let’s explore this further.
The color called purple has roots in the ancient world. Harvesting Bolinus brandaris, a mollusk contains a secretion that when oxidized yields a purple color known as Tyrian purple. In the modern era, creation of coal-tar dyes produced a variety of vivid hues, including purple. Modern synthetic and mineral purple hues are a fundamental part of nearly every line of paint. The notion of a color we identify as purple has been around for a very long time.
The history of purple draws references to politics and religion when exploring the origins of the use of this hue. We find grizzly stories from the past about fatal implications if anyone outside of royalty was caught possessing purple garments. Christianity employs purple to symbolize sacrifice and mourning in the ecclesiastical season known as Lent. Examining purple, specifically for its hue/spectral properties takes us down an interesting path.
I find that purple is one of several hues that has a pronounced shifting color bias. Even more confusing, the same color sample can appear to be warm when compared to a different purple or blue hue and cool when another sample of purple or blue is placed next to it. The trick is how much red or blue is contained within the mixture.
References to purple in nature are difficult since purple is not as abundant in flora as other colors. As a point of reference, you can examine for yourselves, let’s use the color employed by football teams to identify the difference between warm and cool purple. A great example of a warm purple is the color used by the Minnesota Vikings. A good example of a cool purple is the raven mascot illustration used by the Baltimore Ravens, focusing especially on the color depicted in the middle of the head of the raven logo. The uniforms have a blue-violet appearance. But, when a Ravens game is televised, the video sensors in the camera appear to have a difficult time depicting the uniforms appearing as purple. Under most conditions, the uniforms look dark blue. One reason could be is that stadium lighting has a very blue bias and that brings out the blueness of the blue-violet dye in the uniforms.
I acknowledge that all colors have a bias, but purple is a good example of a color that shifts dramatically. It is also surprisingly to find that no art materials manufacturer produces a blue-purple paint. The reason being that no single pigment blue-purple exists.
Over the span of modern color making, many purple hues have come and gone. In the past, several dyes were given color index numbers and were used to make artists’ paints. Rhodamine Violet, Anthraquinone violet, Alizarine Violet along many others were the first purple colors to be produced. None of them remain in today’s paints for artists.
The stock and trade of violet pigments appears to have settled into a group of warm purple colors. Most manufacturers of paint produce Cobalt Violet PV14, Ultramarine Violet PV15, Manganese Violet PV16 (for cosmetic use) Quinacridone Violet PV19 (plays a dual role as purple or magenta – dependent on the art materials manufacturer) and Dioxazine Violet PV23.
A search of these violet pigments and others do not reveal violet with a blue bias, or in other terms, a single pigment blue-violet hue. Some mixed colors exist that combine purple with blue to create what they call a Blue Mauve.
In preparing a 12-step color wheel, depicting a blue-violet is easy. The same for creating a red violet. The vexing issue is creating a purple with no apparent color bias towards blue or red. Can a purple without a red or blue bias exist? No matter what adjustment is made to the color, it always appears warm, despite having a cool and warm mixture on either side of what should be a neutral purple. The 9 square illustration shows: Row 1 – warm purple, cool purple, warm purple. Row 2 – medium blue, cool purple, medium blue. Row 3 – cool blue, cool purple, cool blue. As adjacent blues get cooler, the cool purple becomes warmer. The opposite visual phenomenon exists. As adjacent purples get warmer, the cool purple becomes cooler. To see this best, cover over the rows that are not being examined so that only one row is showing. (The same exercise using very warm colors in the central position of the 9 square grid, make a difficult time of “bending” colors like yellow or orange to appear cool.)
So, for the sake of completing this argument and this essay, my vote is to say that an unbiased purple is either difficult or impossible to render. In mixing color, equal parts of blue and red are not the solution because each pigment has a different tinting strength and equal parts of each become a useless exercise.
This argument is better left alone. When rendering purple, the bias will reflect the need for either a warm or cool purple and the ability to mix either warm or cool violet is easily achieved using a combination of blue and red or manipulating an existing single-color purple to shift to warm or cool by adding red or blue to it.
Color bias is fundamental to making art and every artist has their own method of handling and adjusting to account for the color of the light in a scene and shadows to determine the warmth or coolness that is necessary to render a passage in a composition.
The Syntax of Color