Borax (Sodium Tetraborate)

Borax (sodium borate or sodium tetraborate dodecahydrate, Na₂B₄O₇·10H₂O) is essential in making milk or casein paint and glue. You can find the paint recipes below.

Sodium borate is an important boron compound as well. It is a soft, white, many-sided crystal that dissolves easily in water. If left exposed to dry air, it slowly loses its water of hydration and becomes the white chalky mineral tincalconite (Na₂B₄O₇·5H₂O) or sodium tetraborate pentahydrate. Commercially sold borax is usually partially dehydrated and is typically available as 10 Mol (dodecahydrate), 5 Mol (pentahydrate), and anhydrous (completely dehydrated). 

Storage

No special handling precautions are required. Dry, indoor storage is recommended.

Health and Safety

Wear dust masks to avoid inhalation of dust. Occasional mild irritation effects to the nose and throat may occur from inhalation. Refer to the Material Safety Data Sheet.

Environmental Hazards

Large amounts of this product can harm plants and other species. If it is spilled, comply with Federal, State, and local regulations on reporting spills. For further details, refer to the Material Safety Sheet and labels.

Origin and History

Just how long man has used borax is unlikely to be resolved. According to legend, Babylonians brought borax from the Far East more than 4,000 years ago to be used by goldsmiths, and writings have frequently cited ancient Egyptians as using it in metallurgy, medicine, and mummification, but none of this can be substantiated. The nitron baurak of the Greeks, the borith of the Hebrews, the baurack of the Arabians, the boreck of the Persians, and the burack of the Turks might all appear to express the same substance, borate of soda (i.e., borax). However, there is little evidence to show when or whether these names described the substance we now know as borax (Na₂B₄O₇·10H₂O). In fact, they are all transliterations of the Arabic word meaning "glitter" or "shine."

It seems probable that real borax was known to and used by artisans, scholars, and alchemists of the Islamic civilization before 800 CE, and it is possible that Harun-al-Rashid's traders transported borate to China around that time; however, if so, its origin is unknown. It wasn't until the Middle Ages that borax from Tibet was regularly imported into Europe. It was very expensive, and this limited it principally to the precious metal trade. Goldsmiths used it as a soldering agent and in the refining of metals and assaying of ores. The quantities traded were small, its production method was secret, and its source remained a mystery until the second half of the 18th century.

By the early 1500s, glass making was widely practiced in Europe, however there are no references to the use of borax. In trying to fix the first use of borax in glass, it must be remembered that prior to the 19th century, many glass accounts were written by observers who were not themselves involved in the art. Technical secrets were passed on by word of mouth and practical instruction, and those who knew most were not given to writing for the benefit of others.

The earliest reference to borosilicate glass comes from China, where Zhao Rukuo described glassmaking by Arabs and others in 1225: "Borax is added so that the glass endures the most severe thermal extremes and will not crack." The earliest European mention of borax in glass occurs in a German work by Johann Kunckel in 1679, giving recipes for artificial gems.

In 1739, another German, Johann Cramer, recommended three parts of prepared flints (silica), one part of the purest alkaline salt (potash), and one part burnt borate (borax) for crystal glass. In 1758, Robert Dossie reported that the best-looking glass plates contained 56 percent white sand, 23.5 percent pearl ashes (potash), 14 percent saltpeter, and 6.5 percent borax. He also noted that borax helps glass receive specific colors.

Source

Borax is a complex borate mineral found in playa lakes and other evaporite deposits. The basic structure of borax contains chains of interlocking BO₂(OH) triangles and BO₃(OH) tetrahedrons bonded to chains of sodium and water octahedrons. Most old mineral specimens of borax are chalky white due to a chemical reaction from dehydration. They have actually altered (at least on their surface) to the mineral tincalconite, with the loss of water. This kind of alteration from one mineral to another leaves the original shape of the crystal. Mineralogists refer to this as a pseudomorph, or "fake shape," because the tincalconite has the crystal shape of the predecessing borax. Borax is directly deposited in arid regions from the evaporation of water in intermittent lakes called playas. The playas form only during rainy seasons due to runoff from adjacent mountains. The runoff is rich in the element boron and is highly concentrated by evaporation in the arid climate. Eventually, the concentration is so great that borax crystals and other boron minerals form.

The most commercially important deposits are found near Boron, California, and other locations in the southwest of the United States, such as the Atacama Desert in Chile and Tibet. Borax may also be produced synthetically from other boron compounds.

Uses

Borax is widely used in detergents, water softeners, soaps, disinfectants, and pesticides. It is used to make enamel glazes and glass and strengthen pottery and ceramics. It is also easily converted to boric acid or borate, which has many applications. A mixture of borax and ammonium chloride is used as a flux when welding iron and steel. It lowers the melting point of the unwanted iron oxide (scale), allowing it to run off. Borax is mixed with water as a flux when soldering gold, silver, etc., in jewelry. It allows the molten solder to flow evenly over the joint in question. Borax is an ingredient in Slime.

Borax is also used in the hydrolysis of casein to make milk paint. Casein acts as the binder for the pigments and is a natural component of milk. It is made by precipitation from milk with enzyme or acid and is then reconverted into glutinous casein glue with the aid of an alkali, such as borax. Casein is one of the first binders ever used by humankind. Casein can be painted on various surfaces, including wood and plaster. Whatever surface is used should be rigid, as casein is too brittle to paint on flexible surfaces, such as canvas. Casein is also an emulsifier that allows you to combine oil and water. Of the methods of making casein paint, borax casein is easier to use and better suitable as an artist-grade pigment binder. It is used to make paint commonly known as casein tempera, but it can also be used to make larger quantities of interior wall paint.

Recipes

Borax Casein

Ingredients by weight:

2 1/2 oz. (80 g) casein powder
9 fl. oz. (250 ml) cold water
1 oz. (32 g) crystalline borax
9 fl. oz. (250 ml) hot water

Ingredients by volume:

5 parts of casein powder
9 parts cold water
2 parts crystalline borax
9 parts hot water

Directions

Soak casein powder in cold water in a covered container overnight. Dissolve borax in hot water. Add the prepared borax solution to the casein solution and stir. Hydrolysis will start right away and must be completed before the next step. Wait about two hours until no more swelled casein particles can be seen and the yellowish mass is evenly translucent. Heat the solution in a double boiler until it becomes liquid (140° F). Once the solution has cooled, it will return to a syrupy consistency and is ready to be used as a pigment binder. As with all water-based media, the chosen pigment has to be wetted first. This is achieved by adding small amounts of water to the dry pigment. Then, using a palette knife or spatula, the water is worked into the pigment until it retains a paste consistency. The casein solution is then added to the color paste sparingly. The casein-to-pigment ratio cannot be described in exact proportions. The amount of pigment varies according to the desired opacity. The amount of binder (casein solution) varies according to pigment. Before use, apply small amounts to a piece of cardboard to ensure a sufficient amount of binder. Add more casein solution if the pigment comes off after a gentle rubbing. Once pigment and binder have been combined to the desired consistency, the resulting paint can be thinned with water.

Casein is a natural product that will spoil if kept wet—store unused casein solution in the refrigerator, which should preserve it for up to two weeks.

Casein Gesso

Ingredients

9 parts borax casein (see above)
4 parts chalk
4 parts Titanium white pigment

Directions

Combine chalk and pigment. Slowly add the mixture to the borax casein. Mix until smooth. Strain gesso through a cheesecloth to ensure that there are no lumps. Apply in thin layers to a panel sized with borax casein. Casein Gesso makes an excellent ground for any paint; it is perfect for casein paint.