Transparent vs opaque colours

I often get questions that start with “This might be a stupid question but…”

Stupid questions are the essential ones; the questions people are worried about asking because they think everyone else knows the answer. But they don’t! And they really wish they did, so don’t be afraid to ask…

Our third question comes from Stella, who was at my West Dean course in September: what exactly is the difference between transparent and opaque paints and how does it affect my paintings?

The answer is that transparent paints let the light through to the underlying paper while the opaque paints reflect the light, effectively blocking it and stopping it from reaching the paper. The effect is that transparent paints have a more glowing, three-dimensional finish thanks to the resulting layering, while the opaque paints have a flatter, matt appearance.

Some media such as gouache, chalks and pastels will always be opaque, because the medium itself is opaque.

Other media such as watercolours, oils and acrylics are transparent, so the transparency/opacity of the paint will depend on another factor, which is the pigment used in each colour.

When it comes to transparency, there are 4 categories of pigments:

  • Transparent, which let all the light through
  • Semi-transparent, which let most of the light through but reflect a small part
  • Semi-opaque, which reflect most of the light but let a small amount through
  • Opaque, which reflect all the light and let nothing through

Here are some examples of what this means in practice.

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Case A – A single wash of transparent blue over white paper

The light goes through the paint, bounces off the paper and comes back through the layer of paint. The eye sees the blue colour, with a bright finish thanks to the brightness of the white paper underneath.

Case B – A single wash of opaque red covers the paper

The light bounces off the paint without allowing it to travel through to the white paper. The eye sees the red colour, with a flatter finish because of the lack of depth.

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Case C – Three layers of transparent paint over white paper

The light travels through all the layers, bounces off the white paper and comes back through all the layers. The eye sees all the colours at once, with a lot of depth created by the layering.

Case D – One opaque wash of green between two layers of transparent colours

The light goes through the yellow layer to the green opaque layer but cannot go any further. The eye will see the green through the yellow, giving a yellowy green colour with some depth, but the grey layer and the white paper will disappear entirely, limiting that depth and annihilating the white paper-given glow.

Now it’s up to you to play with all the above, combining your pigments to reach your desired effects. Remember that this will only work in a transparent medium. If the medium is opaque, only the top layer will be visible no matter what pigments are used.

Examples of transparent colours: all the Quinacridones and Phthalo colours, Permanent Rose, Gamboge and Indian Yellows, Perylenes and most blacks.

Examples of opaque colours: all the Cadmiums, Cerulean Blue, Naples Yellow and all whites.

Lemon Yellow and Sap Green are the troublemakers. Depending on the brand, some are transparent and some are opaque. I will write about them in the Pigment Spotlight section in different posts.

There will also be follow-up posts about Optical Mixing and Harmonic Shadows, which are two techniques deriving directly from the transparency/opaque dichotomy.

Keep the questions coming; I will answer them, whether directly or with a blog post or video.

Happy painting!

 

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Pigment Spotlight- The non-granulating French Ultramarine aberration

When I heard that there was a new, Non-granulating French Ultramarine, my heart missed a beat. It definitely didn’t feel right.

I had that feeling you get when a long trusted and beloved friend does something so bad you didn’t even know they were capable of it.

My favourite blue had stopped behaving like it should and my understanding of pigments was being tested.

It reminded me of the story of the fox and the scorpion. A fox is about to swim across a river, when a scorpion asks: “Please can you help me? I need to get to the other side of the river but I can’t swim. Will you carry me on your back?” The fox is not too keen on the idea of carrying a lethal creature on his back. “How do I know you won’t sting and kill me?” “Well, it would be very stupid of me. If I sting you while you swim across the river, you will drown and I will die with you.” The argument seems irrefutable, so the fox agrees to help the scorpion. As they reach the middle of the river, the scorpion stings the fox. With his last breath, the fox asks: “Why did you do this? In a few seconds I shall be dead and you will die with me!” The scorpion answers simply: “I am so sorry, I couldn’t help myself, it is my nature…”

French Ultramarine granulates; it is its nature.

With some trepidation, I started my research into the so-called non-granulating French Ultramarine. Within a few minutes I was relieved.

Non-granulating French Ultramarine is NOT French Ultramarine at all. It is a mixture of Phthalo Blue (a very good non-granulating blue) and Dioxazine Violet, a controversial violet that has not performed well in lightfastness tests when used in watercolours.

The pigment French Ultramarine PB29 doesn’t even appear in the formulation. It couldn’t, because it would make it granulate! Granulation is its property, its quality, its raison de vivre. You can’t take that away from it. Like the scorpion who can’t help stinging the fox, French Ultramarine can’t help granulating. The extent of the granulation varies depending on the technique used, the paper’s texture and which other paints are mixed with it, but it never disappears. As French Ultramarine was invented as a substitute for the celestial Lapis Lazuli pigment- which itself granulates enthusiastically- it doesn’t really make sense to want the annihilation of the granulation process anyway.

Because PB29 is not part of this paint at all, it absolutely shouldn’t be called French Ultramarine. This is, at best, misleading. At worst, a dishonest market strategy to sell a new paint. It could be called French Ultramarine Hue, which is what manufacturers do when a paint is the colour of a particular pigment but doesn’t actually contain any of it. Even better, it should have a completely new name, without highjacking the fame and success of the long trusted – and bestselling- French Ultramarine.

I also object to the fact that this is a mix of two pigments, which is a step backwards compared to a single-pigment paint, especially as one of the two is unreliable.

If you want a non-granulating violet-biased blue, Phthalo Blue Red Shade (or Winsor Blue Red Shade for Winsor & Newton) is the best one. It is pure, not granulating at all, intense and lightfast. You can add a touch of Permanent Rose if you need your blue to be more on the violet side.

Don’t fall for the Non-granulating Non-French Ultramarine deception. It’s a chimera. Enjoy the liveliness of a beautiful, pure, genuine, granulating, PB29 true French Ultramarine.

Ratings:

Useful range of colours                   0/5

Sufficient lightfastness ratings      1/5

Level of saturation                           2/5

Irreplaceability                                 0/5

Total: 3/20

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