Describing Glass Color 

First and foremost, the statement "Color is subjective." is not 100% accurate. If color truly was "subjective", ink and paint manufacturers would not have devised precise mathematical formulas for mixing pigments to arrive at exact mathematical colors. Instead, they would just mix pigment until it "looked right" to them, and the world would be a cavalcade of "pretty close" color matches. There would be no need for master Lithographers in press rooms, and Pantone would go out of business.

Color is not subjective, our perception of it is.
With all due respect to the accuracy of color descriptions used by dealers and collectors, we know that human perception of color can range from "color blindness" (an actual condition that blocks the perception of any color at all) to the trained eye that keenly distinguishes the most minute nuance of shade and hue. With all the degrees of separation that exist between these two extremes, it only stands to reason that the perception of color varies from person to person.

Color is actually a byproduct of three factors: The light source, the object and the observer.
If we rule out the imperfect eye of the observer, and have a standardized light source reflected upon flat, solid, 2-dimensional color, we can certainly establish exact color attributes. What makes glass more complex is the fact that it is both 3-dimensional and translucent, allowing light to pass through it, and in some places more so than others. Because of the crude manner in which colors were produced in the manufacturing process, antique glass can be far from uniform--color, and depth of color, can vary from one area to the next, usually referred to as "shading".

In a spectral analysis of color there is a fixed, consistent light source, a spectrometer, and a representation of color, beginning with white (all light energy is reflected) at one end of the spectrum, and black (all light energy is absorbed) at the other. Similarly, glass color can vary in depth or darkness, also referred to as density..

Density of Color
With glass, the spectrum ranging from "flint (clear) glass" at one end and "black glass" at the other is a fairly close representation of the bottle color spectrum from "lightest" to "darkest" and evokes terms like those in the chart below, describing the density of color, where color is present.

Using the chart above, you could apply these density values to any color, like green for example, keeping in mind that these densities can be used to describe part of the bottle, or the bottle as a whole. For example, the description: "Clear medium-green, shading to dense yellow-green at the base" could easily be an accurate description of a bottle that is predominantly light green with a yellow tone, gradually deepening in color to a deep green with yellow tone at the base. It is often the case that shading occurs due to the irregular thickness of the glass (a byproduct of the crudity of manufacture) whereby the glass color density increases with it's thickness.

Tone or Hue
The colors in the chart above were used by picking a color in my web authoring color chart beginning with white in the "Clear, Colorless, Flint Glass*" box. In the "Light, Pale, Translucent" box I chose a green color with a decidedly yellow tone {E3,EE,DB}, yet when placed against this yellowish background--I don't "see" much yellow until I gradually darken the color. On my monitor I see the yellow tone clearly in the "Deep" color box, but the hue or tone is mathematically the same from beginning to end.

When we talk about hue or tone, this is the secondary color that takes us from the the basic primary colors to all the nuance of antique glass coloration. "Yellow green" or yellowish-green is used to describe a predominantly green color with a yellow tone, and is synonymous with that description, whereas "greenish yellow" is a term used to describe a predominantly yellow color with a green hue or tone. As colors become more descriptive, these references to hue, tone or "cast" can become more complex, like, "Olive green with strong yellow tones in the middle of the bottle, shading to a deep, yellow green in the base and applied top". This is not meant to confuse, but rather to more accurately detail the nuance of color. The description might add how it looks in reflected light, vs. how it looks in a window with natural sunlight behind it. All attempts to clarify the characteristics of color, density and shading. When green meets blue, a common juncture for antique glass, all manner of descriptions arise from aqua to greenish blue to teal green (bluish-green leaning towards green) to teal blue (greenish-blue leaning towards blue) and all points in between.

More on color to be continued as time allows, this is just a brief primer - in the next update, we'll look at real examples and try to describe them, as well as more information on tone, hue and other external influences that can cause the display color of an antique bottle to vary.

* You will notice that I left "milk glass" out of the chart above. Milk glass, like pottery jugs or ginger beers are not generally rated according to color or density variations, whereas black glass generally is, so I will exempt milk glass from any discussion of color for now.