Knowing the properties of the pigments used to make your watercolours makes it possible to guess which colours are opaque and which transparent. If the micro-particles of coloured pigment are extracted from metals, eg Cadmium Red, Cadmium Yellow, or Cobalt Blue, you can guess that the minute pigment particles would be fairly dense and therefore likely to be somewhat opaque, whereas those extracted from carbon (eg Permanent Rose and Permanent Sap Green or the polysyllable names like Quinachridone Red and Indanthrene Blue), can be rightly guessed to be transparent since carbon is a lightweight organic material. Likewise, in diffusion, the metal particles are heavier and spread out less rapidly than the lighterweight carbon particles.
Good composition is crucial to the success of painting, but if you are painting outside, planning and drawing for too long can delay catching the very light that attracts you to a subject. You can go straight in with pale washes to establish the composition, especially if short on time, or if a drawing is required to position items, make it a guide for the brush, to tell it where it can and cannot go. You can always draw more detail into a watercolour as you go along, don’t waste precious time at the start on detail that may quickly be covered up, especially in the shadows. If you begin from the middle of the paper or with the thing that most interests you, it may not matter if the rest is unfinished when you have to stop.
Many painters get hung up on anxiously trying to match, as closely as possible, the colours in their painting to the colours in their subject. Worry less about the actual colours of your subject and concern yourself instead with the relationships between the colours within your painting. Matisse says it perfectly: “There can be no colour relations between it (your subject) and your picture; there are the relations between the colours in your picture, which are the equivalents, substitutes or representations of the relations between the colours in your model."
Artists often talk about "painting the light" but In watercolour we have to not paint the light to "paint the light"!!! With watercolour the untouched paper represents the lightest lights and white so we have to paint the area around the light or white to bring it into being, ie in order to paint the light a watercolourist must paint the shade!
[Cobalt Blue is a warm semi transparent blue, ideal for the limpid shadows that play over white petals.]
Red is a powerful colour. Its rarity value in nature attracts attention. For the artist, red’s inherent mid tone sits satisfyingly between the light tone of yellow and the dark tone of blue and this marriage of mid tone with resonating hue delivers impact to a painting with even the smallest dash of red.
Choose your red not only for its hue but also for its opaque or transparent properties: for example a setting sun or red flower might call for the radiance of a warm transparent red, such as Quinachridone, whilst a red robe or red bus might demand the brilliant punch of an opaque red like Cadmium.
The illusion of space in a painting is created by perspective and tone. The horizon is always at eye level and all lines leading away from the eye eventually meet at the horizon. Similar sized objects, as they recede, look smaller and lighter in tone in relation to each other. Thus objects in the foreground appear larger than their equivalents in the background. The viewer has no problem believing this relationship because they have seen it in real life, so you only need put the suggestion into their mind to enhance the perception of space in your painting. The greater the difference in size the more distance suggested.
Use your subject as the excuse to paint a watercolour, rather than your watercolour as a medium to paint the subject. The appearance of the watercolour on the paper is way more important than likeness. Lifeness, not likeness, should be the aim of your painting. However well you paint the sun or an apple it can neither warm nor feed you - a painting is not pretending to be something, it is something: something other than what it represents. Freed from the obligation to make a likeness, the painter creates something new that did not exist before: a new lifeness.
Imagine you are allowed only 50 brushstrokes per watercolour painting. You would take care to get each one right, you would make sure that each time you laid your brush down it carried the desired colour to the chosen place and made the required shape – no dithering with meaningless marks or insipid layers of colour. You would spend more time mixing in the palette and more time looking at the subject. In a successful watercolour more time is spent off the paper than on it!