Before they are dry, acrylic mediums appear milky-white. When dry they become perfectly clear. They can be added to acrylic colours without limit.
The three clear mediums have been formulated to have different viscosities. By diluting the gel medium with water you will create a liquid which may have the same consistency as fluid medium, but because it will contain less resin solids it will create a weaker and thinner film when dry.
Artist’s quality paint is formulated to have maximum pigment loading. We put as much ground pigment in the acrylic resin as is possible in relation to the properties of each individual pigment. While artist’s colours can be used straight out of the tube or jar, using a variety of clear mediums can vastly increase the range of effects that can be achieved. Because artist’s paint is a highly concentrated product, clear mediums can be used to extend the paint, to make it go further. This is especially true when working with more expensive, high tint strength colours, like dioxazine violet, for example. To extend the paint without considerably altering its viscosity, matte medium is a good choice. Adding gel medium will make the paint slightly thicker, while fluid medium will create a fluid paint.
Some colours are so strong in tint strength that they look very dark, almost black, in their unaltered form. By adding clear acrylic medium it allows the colour to be more visible by making a more transparent film. By adding clear medium to the paint and applying it in layers you can achieve a depth of colour and a type of colour mixing that is not possible in any other way. This technique is called glazing, and is particularly effective with high tint strength, transparent pigments like phthalos and quinacridones. Fluid medium is suitable for use in this technique because its flow properties allow thin, even layers to be made easily without holding brush strokes. Because acrylic is fast drying, it is a convenient material for this type of painting.
Artist’s colours are made up of two main ingredients, pigment and acrylic resin. The acrylic is the binder that holds the pigment together in a strong film. Clear mediums are essentially paints without colours. Acrylic resin is methylmethylacrylate, the same material that is in acrylic sheeting, known as plexiglass or perspex. Unlike most other plastic resins, acrylic has outstanding lightfastness and weatherfastness. Most other plastics break down in ultraviolet light exposure, and are subject to yellowing and brittleness. Acrylic’s resistance to ultraviolet light and outstanding optical clarity make it a top quality artist’s material. It is one of the clearest substances available.
For these reasons clear acrylic mediums are suitable as a “varnish” type coating for finished work. Because different pigments have different sheens, some areas of a painting may appear shinier than other areas. Artists sometimes prefer to unify the sheen of a finished painting by applying a layer of clear medium to its surface. Using fluid medium as a clear coat will make the colours appear more saturated because its sheen is glossy. Using matte medium as a clear coat will diminish glare. It is only the sheen of the last layer applied to a surface that will determine its final sheen.
Since they don’t yellow or get brittle, these mediums are also suitable as a final protective layer on top of papier-mâché and mixed media work. They are especially useful in collage and decoupage as they perform both as an archival quality adhesive and as a clear coat.
While gesso is more usual in preparing canvas for painting, clear mediums can also be used. In order to create a complete seal the first layer of medium can be diluted with water so that it can soak in and penetrate the fibers of the fabric. Subsequent layers should be used full strength.
Oil painters usually have several types of oil on hand as well as turpentine for diluting. Acrylic painters will get the most out of their colours, and broaden their repertoire of techniques when they have different types of clear acrylic medium available to modify their paints, as well as water as their dilutant.