Wikipedia summarizes gouache thus:
Gouache...body color, opaque watercolor or guache, is one type of watermedia, paint consisting of pigment, water, a binding agent (usually dextrin or gum arabic), and sometimes additional inert material. Gouache is designed to be used with opaque methods of painting. The term, derived from the Italian guazzo...Not the best summary, but a place for me to start.
Entering the term into the Oxford Reference search box and limiting it to "Art and Architecture", brings up 582 entries. Imprecise, but some of the references might work for me.
More concisely my 1971 Painter's Dictionary Of Materials And Methods, by Frederick Taubes says:
Gouache is a term used for opaque watercolors that use white color, not the white of the paper, for achieving white or light passages. Hence, standard transparent watercolor mixed with white, as well as colors that are cut with white in their manufacturing process, are referred to as gouache. ... To manufacture gouache, colors are mixed with a white pigment such as whiting. Their binder is, as a rule, gum Arabic. pp.120, 121But what's the difference between gouache, watercolor, and body color?
Handprint, an informative personal website by the artist Bruce MacEvoy, details anything relating to watercolor pigments and manufacturers. MacEvoy describes gouache and distinguishes between the terms.
The method of mixing watercolor pigment with an opaque white pigment in a watercolor vehicle (made with gum arabic) is traditionally referred to as gouache. The method of mixing concentrated watercolor pigments with a vehicle that is made with fish gelatin (isinglass jelly) or animal gelatin (size) — without the addition of any white pigment — is traditionally called bodycolor (or distemper in England). However, the two terms are sometimes confused or used interchangeably, both in historical writings and current usage: some "designer's gouache" paints are made with concentrated pure pigment in a watercolor vehicle, without any added white pigment. The core meaning in all cases is that gouache or bodycolor is an opaque watercolor paint.
The Handprint website goes on to say
Gouache is usually made with the same gum arabic vehicle as ordinary watercolors. A good quality gouache contains the following ingredients:
• dry pigments
• distilled water
• inert pigment (blanc fixe or precipitated chalk)
• binder (gum arabic)
• plasticizer (glycerin and/or dextrin)
Sometimes a wetting agent, such as ox gall, is also added to improve milling or handling characteristics. Dextrin, a syrupy medium derived from heated corn or potato starch, is also sometimes used to make the texture of the paint creamier.
Ralph Mayer 1980 book The Painter's Craft: An Introduction To Artists' Methods and Materials tells me thatWith the exception of the impermanent, "brilliant" pigments ... the pigments used are the same as those found in transparent watercolors.
A gouache painting is a watercolor done in opaque instead of transparent coloring.... The materials used to make gouache and watercolor paints are identical or nearlyso, the difference between them lying in their method of preparation. Gouache pigments are ground with a greater proportion of vehicle to pigment, and when they are painted out, the result is a continuous paint film of appreciable thickness rather than a thin wash or stain produced by watercolor.
The color of the paper usually has little effect on gouache paint as an underlayer... p.133
Inert pigments, such as blanc fixe or chalk, are often ground in with some of the colored pigments, not as adulterants but in order to increase their bulk and to improve their brightness or opacity. Those colors which are ordinarily transparent in oil and watercolor act as body-colors in gouache, and often yield womewhat different color effects. p. 135
|Abrect Durer's Hare|
In the SCA period, gouache was not recognized as a separate paint type (as oil and acrylic are today). The term is first found in late period as a technique of mixing pigments with the binder gum Arabic, some color recipes specifying the addition of chalk or eggshells.
Below are related recipe bites from the 1410 century source "Manuscripts of Jehan le Begue", that describe combining an opaquer with pigment.
A good rose color...for parchment or paper... --Take brasillum [process it then] let it be put into a glazed jar with white chalk or gersa [gesso] in powder or with powdered bracha...which is otherwise white lead, otherwise ceruse, otherwise Spanish white and let it be allowed to incorperate with the said chalk or ceruse. ... And write and draw and paint with this colour whatever is wanted on parchment, and primed panels, as well with the pen as with the paintbrush. And the less ceruse or chalk there is in it the darker will be the colour; and so, on the otherhand, the more there is of it the lighter the colour will be. Merrifield vol. 1 p. 270.
A blue color, that is azure, which is not ultramarine...which is good on ...parchment, or paper...--Take fine indigo, which is call by the name of Bagadel, and Spanish white, otherwise called ceruse or blacha, and mix both together, and grind them on a hard stone, with white of egg beaten and mixed with pure water, or with gum water, made with gum Arabic...And the lighter or less dark you require it, the more blancha or ceruse you must mix with it; and on the other hand, the darker you wish it, the less you must put of the said ceruse, that is, white-lead, that is to say, while you are grinding the colour upon the stone. Merrifield vol. 1, p. 271.
Begue's comments tell us that opaquers were added, but don't add too much or the color will be too light. What today is called a tint. (The color theory, as we know it was not developed until the early 19th century.)
They were also aware of two color "densities", at least by the 16th century as the Manuscript of Diverse Secrets tells me:
Divers colours for painting works in oil, or "a putrido"-- And mark that the colours are of two kinds, one of which consists of those which have not body, and which do not conceal the colours laid under them, but only tinge them, as saffron for inatance; the other consists of those which have body and which cove every other colour over which they are laid, and many of these colours are inimical to each other, so that by mixing together they spoil each other, as white lead and verdigris and white lead and orpiment. Merrifield vol. 1 p. 608.This also showed that white lead could not be used as the opaquer for every color. It would spoil verdigris and opriment (which is also why it wasn't used by illuminators to highlight those colors).
And from the 16th century Booke of Secrets you find:
Of Red color, and first of Brasill: ... then put in one ounce of beaten alum, one ounce of gum Arabike, two ounces gum of a Cheritree, or else two ounces of cleane glue, strain it from the wood: you may likewise put into it some chalke beaten to pouder. p.8
A faire greene colour: Take honie, put a little quantitie of vineger more then the honie is, into it, mingle it well in a leaded or copper pot, stop it well, and set it 12 daies under another pot, and put thereto a little chalke. p.11
To make Azure: Take one ounce of white lead, nine ounces of Indicum, pour good vineger unto it, put them in a leaded dish, let them seeth well, and that which swimmeth on the top is the color. Or take two parts of chalk made of egshels, one part of Verdgreece, one part of Salarmoniacke, mingle them together with strong vineger, and put them into a new pot, stop it well, that no aire issue forth, set in it a warme place for a month long, and it will be Azure. p.13
To summarize, what I found.
While the term "gouache" is distantly related to the late period Italian word "guazzo", it wasn't used to describe a paint type.
The technique combining a pigment, binder and opaquer to make paint less transparent was written about by the 16th century.
They were even aware by the early 14th century that doing this required care or it would make the color too light. Also, not every whitener could be used with every pigment; white lead would spoil some colors.
In my opinion, modern tube gouache made with a period pigment or safe modern equivalent are an excellent substitute for anyone not seeking ultimate authenticity. The difference between the period materials and today's manufactured gouache depends on the preservatives and plasticizers, added to prevent mold and maintain usefulness. I also take care with the hues I use so the illuminations appear created with period colors.
Unless I'm entering a high-level competition, I make choices based on what is best for the artwork, rather than authenticity. As a scribe working in two worlds, the gouache information is important to know and is useful in documentation.