Mixing with water can be done in two ways:
Alla prima means that the painting is painted 'wet-into-wet'. In this technique you mix colours not only on the palette but also on the painting itself and the paint is applied against and over one another. A painting must be finished while the paint is still wet and so the painting will be built up of a single layer of paint. The paint can be applied pure or with the same thinner all the time. In the latter case the most durable result is produced using Cobra painting medium.
With layered painting you build up the painting from various layers. A next layer can only be applied once the previous layer is dry enough to ensure that it will definitely not dissolve. With a layered painting a technique is followed that is known as 'fat over lean'. Every subsequent layer must contain more oil.
The first layer must be applied lean. For this the paint is thinned with water. During the drying of this layer no compact film of paint is formed, but rather a porous one. Oil from a following layer will therefore be absorbed by the underlying lean layer and so when drying will adhere within the numerous pores. This helps to create good adhesion between these two layers. As an underlying (lean) layer abstracts oil from the top layer, it has to be ensured during painting that the underlying layer has relatively more oil. If this is not the case this will affect the quality of the painting.
In relation to the mutual adhesion the fat over lean principle also has a function in absorbing the tension between the various layers of paint. The painting is constantly exposed to movement; on the one hand due to the flexibility of the grounds such as the artist's canvas, and on the other hand through, for example, changes in temperature and air humidity. For the durability of the painting it is therefore important that all paint layers can absorb these movements. The more oil the paint layer contains the more elastic it will be once dry.
If a painting consists of several layers whereby the under most layers contain more oil than the one directly above, therefore against the fat over lean principle, then the less elastic upper layers will in the course of time pull away from each other by the more strongly moving underlayers. Once this is noticeable to the human eye we refer to it as crackling. This can be avoided by making every subsequent layer a little fatter. The fat over lean principle can therefore also be interpreted as 'flexible over less flexible'. This clarifies immediately why a layer of paint must be sufficiently dry before the next layer can be applied. A layer that is not sufficiently dry throughout is often too elastic for the subsequent layer, with again possible cracking as a result.
The number of layers applied to make a painting is of course a personal choice. It is advisable, however, to thin the first layer with water. The more water, the leaner the layer of paint.
Once the first layer is sufficiently dry, the second layer of paint is applied. As of this point there are various possibilities for continuing further:
1. Thin each subsequent layer with increasingly less water; each subsequent layer therefore contains relatively more oil. You can eventually end up with pure paint.
2. Thin the paint for the following layer with painting medium. A good medium consists of three components: oil, resin and solvents. The oil makes the paint fatter, whilst the solvent ensures that the paint does not become too fat. The third ingredient resin increases the durability of the paint layer. If you build up a painting in more than two layers, you can mix the medium proportionally with water from lean to increasingly fatter. The larger the relative amount of medium, the fatter the mixture. In the final layer you can mix the paint with pure medium.
Whether a painting is painted wet-into-wet or in layers, a glazing can be applied as a final layer.
A glazing can be applied as a final layer; this is a transparent layer of paint the effect of which can be compared with that of a tinted plate of glass placed over a picture: the picture itself does not change, but the colours do.
The reason for applying a glazing may be that a painter is not satisfied with certain colours and wishes to change these without having to paint over the particular section again.
Another reason may be that the painter is deliberately looking to achieve the visual effects of layers of glazing (an enamel-type of top layer and deep colours) and to deliberately use an underpainting as a basis of bringing a painting into the right colour using one or more layers of glazing.
Do not allow brush strokes to be visible in a glazing as you will continue to see these of the underlying layers through the transparent paint; a glazing medium therefore has to flow. Thanks to this property you can also make flowing colour transitions in a glazing.
Of course a layer of glazing has to be more elastic than the underlying paint film as here, too, the 'fat over lean' rule has to be followed. You cannot always foresee exactly how many layers are needed to come to a satisfactory result. Ensure therefore that the paint is never too fat, so that any subsequent paint layer is then still able to bond.
Yes this is possible, providing the following is taken into consideration. By adding a small amount of paint to water you produce a very thin and transparent paint. However if a huge amount of water is added, then the greatly thinned oil does not produce enough protection for the pigments. For a first sketch where later thicker paint or paint thinned with medium is used to paint over it, this is no problem.
If a painting is made only with very thinned paint, it is recommended to add at least 20% Cobra Painting medium to the water. The ground does however have to be prepared for oil paints.
Impasto is a painting technique whereby the paint is applied on to the work in very thick layers. The Impasto technique allows reliefs to be incorporated in the paint layers. Use a palette knife or a brush for this technique.
Cobra is a pure oil paint and can be used over traditional oil paint. If it concerns an older painting that is fully dry, it is recommended that you first wipe it with white spirit or turpentine. The way one continues on the painting depends on the composition of the latest layer of traditional oil paint. The 'fat over lean' rule must also be followed here, whereby it can be assumed that both types of paint are equally fat. The latter also applies to ordinary painting medium versus Cobra water-thinnable painting medium, and standard glazing medium versus Cobra water-thinnable painting medium.
Cobra water mixable oil colour is a pure oil paint and can be thinned using solvents such as white spirit and turpentine. It is then no problem mixing with traditional oil paint. Once the old tubes of 'ordinary' oil paint are finished, you can change from solvents to water. If, however, only water is used, the water mixability will decrease as more traditional oil paint is added to Cobra and brushes will be more difficult to rinse. In order to be able to thin a mixture of Cobra and traditional oil paint with water the paints have to be mixed well using a palette knife and a large part of the mixture has to consist of Cobra water mixable oil paint. The ratio may vary per colour.
This does indeed happen sometimes and is referred to as binder separation. This occurs particularly when there is air in the tube. If so desired, the oil can be mixed back into the paint, or absorbed by for example a tissue.
The Cobra brochure gives an example of a basic palette. Another possibility is to work with just using primary colours plus white: Primary Magenta 369, Primary Cyan 572, Primary Yellow 275 and Titanium white 105. Already with these 4 colours a wide range of colours can be created.