Let’s cover the common ground first. A pigment is a color made from organic or inorganic materials. The colors have different characteristics on their own. Some, like Phthalocyanine Blue, are transparent, some colors like Cadmium Red are opaque, meaning the light cannot pass through the color to the surface of the support. And still others are semi-opaque (translucent), such as Raw Sienna. All of the pigments can be used to make any form of art material you want, be it oil paints or colored pencils.
All paints have three key elements: pigment, binder and a vehicle. Pigments are the color; the binder is an adhesive that sticks the pigment to a surface; and the vehicle helps move the pigment around.
Gouache is an opaque watercolor that is made the same way as traditional watercolors, except with the addition of opacifiers such as chalk, marble dust and titanium oxide. The binder of both gouache and transparent watercolors is Gum Arabic. Gum Arabic comes from Acacia trees.
Basically, traditional gouache is a matte watercolor that can be re-activated with water even when the painting has been finished, similar to watercolors.
Tempera paint is a can of worms and conjures up school nightmares of wondering why the teacher would never give you a blue paint. Red, Yellow, and Green. It took me awhile to figure out why. The teachers were science based and not artistically inclined. Back then, it wasn’t a priority to teach kids anything about art in schools. Perhaps they believed art is subjective and there is no science behind it. Art is in everything, geometry and botany, anyone? From the science school perspective, the color mixing involved light rays, and the light rays of yellow, green, and red. Yellow and green makes blue in the light rays. In pigments however, blue and yellow make green. And that is why teachers never gave you blue tempera paint to play with.
But I digress…
Tempera means to ‘temper’ the pigment to get it to a desired consistency.
Tempera paints are translucent (semi-opaque). This is a very weird medium. At first it acts like an acrylic, and once completed, it acts like an oil painting. Like acrylics, tempera dries to the touch within a few minutes. Like oil paint, it takes a year to fully dry.
Similar to watercolors, tempera paintings should be placed behind a glass , but only for the first year while drying. After the year had past, like an oil painting, it needs to be varnished.
Not all temperas are the same!
Since temperas were around since the beginning of time, they were subjected to a plethora of artistic experiments.
Some are made with gums, oils, some are made with milk, and some are made with eggs, and still others are made with wax! In fact, the poster tempera paint that are used in schools are not actually tempera at all!
So, is it the binder that makes tempera a tempera and gouache a gouache?
Yes, and no.
Traditionally gouache, in order to be a gouache needs to be opaque, and binder based on from the same mixture as transparent watercolors. (Acrylic gouache is different, subsitutes gum for acrylic binders and doesn’t belong in this article.) Tempera tends to be varying in mixtures and are semi-opaque.
Tempera, has an entire history of different experimental binders and vehicles.
Tempera also known as Egg Tempera back in the good old days of painting were made of egg yolk (the binder) and pigment, and moved around (the vehicle) with water. If you can master separating an egg yolk from the sac, then this is one of the easiest paints to make. Most illuminated manuscripts where made with Egg Tempera, and as such, have stood the test of time. It is one egg yolk for each pigment and water. Once you mix it, however, it dries quickly, so you have to use it immediately.
Casein Tempera is different from the other tempera paints because you can use them for impasto, which you cannot with an egg tempera. Caseins are make with milk based products.
Because of the nature of the egg and pigments, only certain pigments are used for tempera paints.
Ready-made bottle tempera or poster paint is a toy for children, and the ingredients vary from manufacturer to manufacturer.
Gum Tempera mixes of gum Arabic or cherry gum, stand oil damar varnish and glycerin.
Wax tempera is made from beeswax.
Oil Tempera is made with egg yolk, stand oil, oil of spike and sometimes gum Arabic, damar resin and linseed oil. Depending on the variation of mixes, the painter can choose to either have the paint thinned with water, or thinned turpentine.
So, I hope this article was illuminating for you!