Borax (sodium borate or sodium tetraborate dodecahydrate, Na2B4O7·10H2O) is an important boron compound. 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). It is an important ingredient in making milk or casein paint and casein glue.
|Alternate Names:||sodium borate, borate, boric acid, sodium tetraborate|
Origin and History
Just how long borax has been used by man is a question 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 to "glitter" or "shine."
It seems probable that real borax was known to and used by craftsmen, 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 method of production was secret, and its source remained a mystery until the second half of 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 needs to be remembered that prior to the 19th century, many accounts of glass 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 for crystal glass three parts of prepared flints (silica), one part of purest alkaline salt (potash), and one part burnt borace (borax). In 1758, Robert Dossie reported the best looking glass plates were ones containing 56 percent white sand, 23.5 percent pearl ashes (potash), 14 percent saltpeter, and 6.5 percent borax. He also notes that borax helps glass to receive certain colors.
Borax is a complex borate mineral that is 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 crystals of borax and other boron minerals form.
The most commercially important deposits are found near Boron, California and other locations in the American southwest, the Atacama desert in Chile, and in Tibet. Borax may also be produced synthetically from other boron compounds.
Borax is widely used in detergents, water softeners, soaps, disinfectants, and pesticides. It is used in making enamel glazes, glass and strengthening pottery and ceramics. It is also easily converted to boric acid or borate, which have 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 also used 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 mankind. Casein can be painted on a variety of surfaces, including wood and plaster. Which ever surface is used, it should be rigid as casein is too brittle to paint on flexible surfaces, such as canvas. Casein is also an emulsifier this 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 that is commonly known as casein tempera, but can also be used to make larger quantities of interior wall paint.
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
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 make sure that there is a sufficient amount of binder. If the pigment comes off after a gentle rubbing, add more casein solution. Once pigment and binder have been combined to desired consistency, the resulting paint can be thinned with water.
Casein is natural product and will spoil if kept in a wet state. Store unused casein solution in the refrigerator—this should preserve it for up to two weeks.
9 parts borax casein (see above)
4 parts chalk
4 parts Titanium white pigment
Combine chalk and pigment. Slowly add the mixture to the borax casein. Mix until smooth. Strain gesso through cheese cloth to ensure that there are no lumps. Apply in thin layers to a panel that has been sized with borax casein. Casein Gesso makes an excellent ground to use for any type of paint; it is particularly good for casein paint.
|Chemical Name:||Sodium Tetraborate Pentahydrate|
|Appearance:||White, odorless, crystalline solid|
|Solubility in Water:||3.82% at 20° C; 51.2% at 100° C|
|Melting Point:||200° C (392° F)|
|pH:||9.3 (3.0% solution) at 20° C|
No special handling precautions are required. Dry, indoor storage is recommended.
Wear dust masks to avoid inhalation of dust. Occasional mild irritation effects to the nose and throat may occur from inhalation. Refer to Material Safety Data Sheet.
Large amounts of this product can be harmful to plants and other species. If product is spilled, comply with Federal, State and local regulations on reporting spills. Refer to Material Safety Sheet and labels for further details.
|Processing Time||Usually ships the next business day.|
|Size||100 g jar|