The colors I have used in this demonstration are the following:

• New Gamboge. A very fine transparent yellow, somehow staining, excellent for my underpainting and giving warmth and light…
  Mayan Yellow, transparent, excellent for sunlit areas.
• Quinacridone Gold… One of my favorites. Granulating, rich, diffusing beautifully!!
• Raw Sienna and Burnt Sienna. Standard colors in most artists palettes…
• Piemontite Genuine. An excellent granulating PrimaTek color that is used mainly for my darker values and shadows, giving interest, warmth and depth.
• Burnt Tigers Eye Genuine. Granulating, rich color, giving beautiful results when used wet in wet.
• Hematite Genuine. The granulating effects it gives are… unique!
• Imperial Purple. What can I say about this color… I love it! It gives warmth and interest in shadows, and very classy results.
• Moonglow. A fantastic transparent granulating color, which I use a lot in shadows. This gives a beautiful variety of colors when diffused!
• Shadow Violet. Excellent for use in shadows, beautiful in granulating effects.
• Mayan Dark Blue. Rich, warm, dark color which I often use for my deeper shadows and darker passages.

In my watercolors, I always work in many layers. I use all approaches, from wet in wet to dry on dry, depending on the desired effects.

Image 1
I prefer to start using some warm yellowish underpainting. I used a combination of New Gamboge, Mayan Yellow, Raw Sienna AND Quinacridone Gold. I splashed water to create some texture.
I started building some mid-values by using Burnt Sienna, Burnt Tigers Eye and Imperial Purple. They are all excellent to give rich, warm and interesting mid values.
Then, I continued to work some of the darks, using mostly Piemontite Genuine, Mayan Dark Blue and Hematite Genuine.
In the photo I am working in different areas to show how I work. Thus, in the lower part one can see the underpainting / first layers. In the upper part you can see the next layers, building from middle to darker values.

Image 2
Next I started working in all areas. I build gradually the darker areas and shadows. I used Moonglow, Shadow Violet and Mayan Dark Blue, along with some Burnt Sienna, Piemontite Genuine, Imperial Purple and Burnt Tigers Eye to give some warmth in certain parts of the shadows. I work from one area to another, trying to build up the interest, but keep a balanced composition at the same time. This involves several layers…

Image 3
I decided to give more depth to the painting, by “inventing” some more shapes, in order to have a more interesting and balanced composition. This was a decision that was taken while re-evaluating the procedure, although my initial sketch was… more or less what I had painted in the first two images.
Thus, I painted the blue/gray metal surface, the cables and the darker shapes at the back. I took advantage of the granulation of Primatek Colors to have more texture, I spattered, I created various lines to show the mark of time on the metal surfaces…
I finished the painting by gradually building (more) on the contrasts and adding some random “calligraphic” lines and shapes that help in the overall balance of the painting.