I want to start this segment with a challenge. No matter what your medium is, pick any two paints, pencils, pastels, etc. and describe the difference/s between the two without any reference to their color. This exercise will help you understand your medium in new ways.
Two paints can have essentially the same hue (color) but have other differing characteristics. In this experiment I will compare Cerulean Blue and Phthlocyanine Blue in terms of how they act in a mix.
If you follow my blogs, you have seen me refer to two groups of paints in a couple of different ways. Classic/Sinker vs Modern/Floater. The ‘classic’ paints are those that were available before the 20th C, and ‘modern’ are those that originated mostly after the 1940’s. Most of the Classic paints originate from the earth, and have larger and denser pigment particles, which makes the particles sink quickly. The Modern pigments, on the other hand, have relatively smaller and less dense particles that tend to stay afloat in a wash much longer.
What does this mean to the watercolor artist? Simply put, if a Classic Sinker is mixed with a Modern Floater, the two paints will separate as they dry, producing a mix the is two-toned. If two Moderns are mixed, they stay mixed as they dry.
In this experiment I use a Cerulean and a Phthlo blue, which are essentially the same color. The Cerulean is a Classic pigment with particles that sink very fast. Phthalo blue is a Modern pigment whose particles tend to stay afloat until the water in the mix is fully absorbed by the paper and/or evaporated.
In the following photo you can see the differences in the two paints in side-by-side swatches. Note a couple of things: 1) the Cerulean (top) granulates. This is common among the sinkers. Not all sinkers granulate, but ONLY sinkers granulate. 2) the Phthalo is smooth, but has a distinctive ‘edge’. This is what I refer to as an ‘edging paint’. Paints with smaller/less dense particles tend to stay afloat in the pool of water until the water has totally absorbed/evaporated. Any pool of water will have a high point in the middle and low point at the edges of the pool due to surface tension. This means the finest particles will gravitate to the edges of the pool.
We can see this ‘sinking’ effect quite easily if we mix the paint in a clear shot glass and let them settle. In the photo below I have mixed both the paints and let them sit for about 15 minutes. The settling is obvious. The phthalo on the left has not settled at all, while the Cerulean has almost completely settled.
In the next part of the experiment, I mix both of these paints with another Modern – namely Transparent Pyrrol Orange. When fully mixed they both produce the same color – a grayish brown. The photo below shows a comparison of the two mixes after they dry. Note the obvious separation of the paints in the swatch that uses Cerulean (right) versus the homogenous mixture using the Phthalo.
It is easy to tell exactly where I dropped in the Cerulean mixture. Wherever I touched the paper with a loaded brush, the Cerulean went straight to the paper, while the orange separated and ended up with a fairly homogenous covering. With the Phthalo blue, the wash stayed mixed and smooth.
The lesson here is simple: if you want a smooth, homogenous wash, use only modern paints. Their pigment will stay afloat as long as your wash is in the Flow State (water visibly moves when you tilt the paper). This means you can add more paint to make it stronger, or more water to make it weaker. In the end the mix will even out.
On the other hand if you want a more varied wash, with a dual-color look, use a Modern mixed with a Classic.
This example produced a very dull mix (two colors which are complements – blue and orange), but there are many more that can give you a vibrant mix. For example, try Ultramarine (Classic) with a Quinacridone Rose (Modern) for a vibrating violet.