Water miscible oil paint (also called "water soluble" or "water mixable") is oil paint engineered to be thinned and cleaned up with water, thus making it possible to avoid using chemicals such as turpentine, whose fumes may be harmful if inhaled (making it necessary to take precautions, such as using the solvent in a ventilated environment). Water miscible oil paint can be mixed and applied using the same techniques as traditional oil-based paint, but while still wet it can be effectively removed from brushes, palettes, and rags with ordinary soap and water. Its water solubility comes from the use of an oil medium in which one end of the molecule has been altered to bind loosely to water molecules, as in a solution.
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Handling in comparison with other media
The traditional rule of gradation of layers — "fat over lean," or flexible over less flexible — applies to water miscible oil paint as it does to traditional oil, and in this respect the two kinds of paint behave in the same way. However, their handling is slightly different: when thinned with water to a considerably liquid phase, water miscible oil paint tends to feel and behave like watercolor (although, unlike watercolor, and to a greater extent than traditional oil, it may lose adhesion to the ground or support if over-thinned); by contrast, when used as a short paste without water for heavy impasto work, it tends to drag, developing a consistency somewhat "gummier" or tackier than the more buttery one characteristic of oils. At midrange (between short paste and long paste) water miscible oil paint is gouache-like, sharing the properties of both transparent watercolor and opaque oil (in the manner of watercolor, for example, some colors will darken upon drying, the more so as more water is mixed into the paint, and in the manner of oil, the paint film will have some thickness to it). Also gouache-like is the overall effect, which tends to be matte as compared to the glossier oil, but this too is a property that will vary, depending on the pigment used and on any mediums (or diluents) mixed into it, as well as on the pastiness of the paint (as a general rule, the pastier, the glossier). The handling of water miscible oil paint, in summary, changes considerably as it passes from one phase to another: this makes it a versatile medium but, by the same token, it also requires the artist to develop by experience specific skills with which to successfully manipulate it and exploit its range to achieve the desired effect.
The practice of mixing water-mixable oils with acrylics is not recommended, the reason being that oils dry much slower than acrylics. Some brands claim this is possible, but the National Gallery's head conservator has issued a statement saying that such mixture is not suitable for the archivability of a painting, an opinion based on the different oxidizing and drying rates of the two mediums. The result would consist of the two mediums pulling apart and cracking within a short time.
Brands
There are several manufacturers producing water miscible oil paint, including:
Mediums
Although this type of paint may be thinned with water, artists may prefer to use specially prepared mediums for improved texture and control. These mediums improve flow (i.e., make the thinned paint less runny and more easily controlled) and can slow or speed up drying time. Royal Talens also has produced a water mixable painting paste that acts as a thickener as well as transparetizer which will not change the consistency of the paint. There are many documented issues with accelerator products in this category causing cracking and damaging the archivability of the medium.
Winsor and Newton has created a special line of oils, mediums, varnishes, and thinners to complement their “Artisan” brand of water mixable oil colors. This line includes thinner, linseed oil, safflower oil, stand oil, painting medium, fast drying medium, and impasto medium, as well as gloss varnish, matt varnish, satin varnish, and varnish remover. All of these products are certified “AP Non-Toxic” by the Art & Creative Materials Institute (ACMI) in the United States.