Borax

• 1. Introduction

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  Borax, the white crystalline salt also known as sodium borate, helped physicists make the first observation of the pion, a discovery honored with the 1950 Nobel Prize. The researchers used a nuclear emulsion that recorded the tracks of charged particles, and borax was added to stretch out how long those faint tracks stayed readable.

  That is an odd job for a powder that most people meet in a laundry aisle. The same compound serves in metalworking, in laboratories, in pest control and, in some countries, on a list of banned food additives.

  This documentary follows borax from ancient dry lake beds to modern regulators. Where on Earth does it come from, and how did it reach the world's workshops? Why does one substance carry so many names, and why is its textbook formula misleading? And how dangerous is it, really?

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• 2. Tibet To The Mule Teams

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  Dry lake beds in Tibet gave the world its first borax. Native tincal, the naturally occurring form, was gathered there and in Persia and other parts of Asia. In the 8th century AD it was traded along the Silk Road to the Arabian Peninsula.

  Borax forms in evaporite deposits, the crusts left behind when seasonal lakes dry out again and again. Only a few places hold enough of it to mine economically. The most important deposits lie at Boron, California, and at Searles Lake, California.

  Smaller finds are scattered across the Southwestern United States and the Atacama Desert in Chile. Newly discovered deposits exist in Bolivia, and Romania has borax too. It can also be produced synthetically from other boron compounds. Natural borax is refined by recrystallization and sold in the United States and many other countries under the trade name Rasorite-46.

  In the late 19th century, Francis Marion Smith's Pacific Coast Borax Company began promoting a wide range of uses for borax. It sold them under the 20 Mule Team Borax trademark. The name recalled how the mineral was first hauled out of the deserts of California and Nevada. The name borax itself had been traveling much longer than the powder.

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• 3. A Word's Long Journey

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  The Arabic word bawraq, also written būraq or bōraq, appears in Ibn Sayyar al-Warraq's Kitāb al-Ṭabīkh. Arabic in turn seems to have taken the word from Middle Persian bōrag, which also produced the Persian bure.

  English borax, and its earlier Middle English form boras, came from Old French boras or bourras. Medieval Latin offered forms such as baurach, borac and borax. Spanish has borrax and Italian has borrace, so the word fanned out across southern Europe.

  The English words tincal and tincar arrived separately, in the 17th century. One route ran through Malay tingkal. The other came from Urdu, Persian and Arabic tinkār or tankār, which explains why English ended up with two forms. All of these appear to be related to the Sanskrit ṭānkaṇa.

  The naming muddle does not stop with language. The chemical formula usually printed for borax turns out to be wrong in a quiet but revealing way.

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• 4. A Misnamed Crystal

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  Chemists call the common form of borax a decahydrate, meaning ten water molecules for each unit of the salt. Its structure actually holds eight, so it is really an octahydrate. The anion is not a simple tetraborate but a tetrahydroxy tetraborate, in which two boron atoms bond to four neighbors and two bond to three.

  The misnaming runs through the whole family. The so-called pentahydrate is really a trihydrate. It is a colorless solid with a density of 1.880 that crystallizes from water solutions above 60.8 degrees Celsius. It occurs naturally as the mineral tinkhanite, and heating the common form above 61 degrees produces it.

  Heat any hydrate to 300 degrees Celsius and the result is anhydrous borax. This form has one glassy variety and three crystalline ones, called alpha, beta and gamma. Their melting points are 1015, 993 and 936 kelvin, and the alpha form is the stable one.

  In water, borax makes a basic solution. At 0 degrees Celsius a saturated solution holds only 1.99 percent borax by weight. At 100 degrees it holds 65.63 percent. It is notably insoluble in ethanol, yet a 98.5 percent glycerol solution at 20 degrees can carry 52.60 percent.

  The salt is stable enough to serve as a primary standard in acid-base titration. Above 21 degrees Celsius it also conducts protons, most strongly along the b-axis of its crystal. Molten borax dissolves many metal oxides and forms glasses. That habit powers the borax bead test of qualitative analysis, and it is the reason metalworkers reach for it.

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• 5. The Metalworker's Flux

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  Jewelers soldering gold or silver mix borax with water and brush it on the joint. It lets the molten solder wet the metal and flow evenly into the seam.

  Welders of iron and steel pair borax with ammonium chloride. The mixture lowers the melting point of the unwanted iron oxide scale, so the scale runs off the work. Borax is also a common flux for forge welding.

  Tungsten is hard to solder, but borax acts as a flux for pre-tinning it with zinc, which makes it soft-solderable. In casting, borax helps melt metals and alloys, drawing out impurities and preventing oxidation.

  Glassmakers and potters use borax too. It is a component of glass, enamel and pottery glazes. In ceramic slips and glazes it improves the fit on wet greenware and bisque.

  In artisanal gold mining, the borax method uses the salt as a flux to avoid toxic mercury. It cannot directly replace mercury, but it is meant to remove the need for it. Gold miners in parts of the Philippines reportedly used borax in the 1900s.

  Evidence suggests the method lowers environmental harm, recovers more gold from suitable ores and costs less. Miners in northern Luzon in the Philippines use it. Elsewhere they have been reluctant, for reasons that are not well understood, even though the method has been promoted in Bolivia and Tanzania.

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• 6. Poison For Ants

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  Worker ants are the delivery system in one of borax's best-known jobs. The salt is toxic to ants and rats, but it acts slowly. Workers therefore carry it back to their nests, and the poison reaches the rest of the colony.

  Borax also guards against other household pests. Pulverized, it is used against stubborn pests such as German cockroaches. It goes into closets, pipe and cable inlets, wall panelling gaps and other hidden spots where ordinary pesticides are unwelcome.

  Wood gets protection as well. Borax acts as a preservative against wood fungus and, diluted in water, as a woodworm treatment. A 10 percent solution is used to mothproof wool, and the salt also serves as an anti-fungal compound in cellulose insulation.

  Termites present a harder case. Borax is more effective than zinc borate against them, but a 1997 paper concluded that at least 10 percent of a colony must be exposed for treatment to work. In Japan, newspapers treated with o-boric acid and borax were laid under buildings. That practice helped control Coptotermes formosanus and Reticulitermes speratus.

  Decaying wood treated with 0.25 to 0.5 percent DOT also worked as bait for Heterotermes aureus. Even so, the same paper judged borate baits helpful over the long term but not enough on their own to protect a structure.

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• 7. Lab Bench And Classroom

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  Molecular biologists rely on borate ions, often supplied as boric acid, to build buffers. TBE buffer and the newer SB buffer are used in polyacrylamide gel electrophoresis of DNA and RNA. Borate buffered saline, or BBS, appears in coating procedures. Borate buffers at about pH 8 also serve in dimethyl pimelimidate crosslinking reactions.

  Borate forms complex ions with other substances in water, and clinical chemistry exploits this. Paired with a suitable polymer bed, borate separates non-glycated hemoglobin from glycated hemoglobin, chiefly HbA1c. That measurement is an indicator of long-term hyperglycemia in diabetes.

  In elementary school science, borax makes slime. Cross-linking polyvinyl alcohol with borax gives a rubbery polymer nicknamed Slime, Flubber, gluep or glurch. People sometimes mistake it for Silly Putty, but that is a silicone polymer. A common demonstration uses Elmer's Glue, which is polyvinyl acetate based.

  At home, borax is found in the 20 Mule Team Borax laundry booster, in Boraxo powdered hand soap and in some tooth bleaching formulas. It has been used for water softening, though it does not bind hardness cations strongly. The sodium ions it adds do not make water hard, and the method suits both temporary and permanent hardness.

  The list of odd jobs keeps going. Borax tints fires green, buffers swimming pool pH and corrects boron-deficient soils as a micronutrient fertilizer. Nuclear reactors and spent fuel pools use it to absorb neutrons and shut down a chain reaction. Dissolved with heated shellac, it makes indelible ink for dip pens. It cures snake skins and salmon eggs, and serves taxidermists as a preservative. Traditionally it was also rubbed on dry-cured hams to improve their appearance and discourage flies.

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• 8. Safety And Suspicion

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  Borax carries the E number E285 as a food additive, yet that use is banned in Australia, China, Thailand and the United States. American caviar compensates by containing higher levels of salt for preservation. Beyond preserving, borax gives food a firm, rubbery texture.

  Despite the bans, it keeps turning up. In China it has been found in noodles such as lamian, shahe fen, char kway teow and chee cheong fun. In Indonesia it is a common but forbidden additive in noodles, bakso meatballs and steamed rice.

  One study put the lethal dose score for borax in rats at 2.66 grams per kilogram, so it is not acutely toxic. Humans were studied in three groups with heavy borate exposure: workers at U.S. Borax mines and production facilities, Chinese boron workers, and Turkish residents near boron-rich regions. Blood and semen tests showed no signs of developmental toxicity.

  The highest estimated exposure was 5 milligrams of boron per kilogram per day, probably from eating in contaminated workplaces. That was more than 100 times the average daily exposure. Studies have recorded no genotoxicity or carcinogenicity.

  The body takes in borax readily by mouth, well above 90 percent, and excretes most of it in urine. Skin absorbs it poorly, but deaths have occurred when boric acid ointments and bath solutions were used persistently on rashes and open wounds. Fatal cases from swallowing include small children who mistook pesticides for drink and suicide attempts with large volumes of crystals. Severe cases can bring a "beefy" red rash, and milder ingestion causes nausea, vomiting, abdominal pain and diarrhea.

  In the United States, borax has been an insecticide since 1946 under various restrictions. All were lifted in February 1986 because of its low toxicity. The EPA exempted boric acid and its sodium salts from tolerance requirements for raw agricultural commodities. A 2006 re-evaluation found no signs of toxicity, though it flagged possible irritation for children if powder is used to clean rugs.

  Europe took a harder line. On the 16th of December 2010, borax joined the candidate list of Substances of Very High Concern under the REACH regulations. The basis was a revised classification as toxic for reproduction category 1B. Imported products containing it must now warn "May damage fertility" and "May damage the unborn child".

  The European Chemicals Agency proposed adding borax to REACH Annex XIV on the 1st of July 2015. If approved, every import and use in the EU would need authorization. A 2012 review in the Journal of Toxicology and Environmental Health, however, concluded that even the most exposed people stay well below blood levels needed to harm reproduction.

  In July 2016 a draft risk assessment from Health Canada found that overexposure to boric acid could affect development and reproduction. The worry was less about any one product than about many exposures added together. Registrations for certain household boric acid pesticides were cancelled, while others continue with new label directions such as enclosed bait stations and gel spot treatments.

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