Thursday, June 15, 2023

Science of Warm and Cool


In painting, color temperature is such an ambiguous concept. For example: orange vs yellow, which one is warmer? Ultramarine vs phthalo blue, which one is cooler? Artists do not want to quantify their color temperature. Their argument is: color is so relative. We only see a color warmer or cooler with respect to another color. This fuzzy ambiguity bothers my engineering mind. So I went to the field of photography. Lo and behold! I found their concept of color temperature is so crispy clear. They quantified the color temperature using K or Kelvin. The "warm" colors have lower K, while "cool" ones higher K. Therefore: orange is warmer than yellow, violet is cooler than turquoise (so ultra is cooler than phthalo). I found a photographer's temperature scale online, and measured 11 color samples. I plot those samples on the CIELuv (pls ignore this nomenclature except the color scientists) color wheel. I was shocked by what I have found. Ah-ha!! Now I know. (1) For very warm colors (red to yellow, or 1 to 4) the temperature varies with the HUE change. Similarly for very cool colors (turquoise to violet, or 8 to 11). This finding reminds me the "prismatic palette" some artists talked about. They follow the rainbow when they paint. (2) For the moderate warm and cool colors (from yellow to blue, or 4 to 8), the temperature varies with the CHROMA change, then flip the hue at the center of the color wheel to the complementary. I feel this understanding can help us to paint better: when you deal with very warm colors like sunset, you can change temperature by hue shifting. However when you deal with grey and subtle colors, you change temperature by chroma variation. Voila!


julie said...

So very interesting! But somehow the chart posted is fuzzy and I cannot read the words. Can you post this again?
I am learning so much from your color studies. Thank you. Julie Grm

Marcel said...

I have had many discussions with my colleges, because I always told them than cooling a warm color in portrait painting what they are really doing is reducing Chroma.

Now I understand why: if you want to cool a warm orangish color, they add to their color mix either green or blue, thus reducing chroma. Looking it on the (a,b) plane in Lab space, if you go from orange to blue, you need to pass thru the area around origin, thus progressively reducing Chroma.

So when they say "you need green tones" what they really mean is "you need to use low-chroma oranges.


P,D. I am also engineering minded.