Cobalt oxide: Chemistry in its Element podcast

The Chemistry in its Element podcast:
curious tales of chemical compounds This week Mike Freemantle is feeling blue ‘The only use of cobalt is in its oxide,’
wrote German mining engineer Frederick Overman in his book on metallurgy
published in 1852 He observed that when the oxide was
melted with a silicate, a fine blue glass was produced. The molten glass was mixed
with potassium carbonate to create a flux which was then poured into cold
water. The glass solidified and shattered into tiny fragments which was
subsequently ground to form a powdered blue pigment known as smalt. ‘Smalt
or the pure oxide is used for covering and painting glass, porcelain, and
crockery a blue colour,’ Overman noted. ‘It is employed as cobalt
glass in oil painting and in fact serves as a fine permanent blue color in all
instances where such a colour is needed.’ Overman spent part of his career working at
an engineering establishment in Chemnitz a city in the German state of Saxony
that is surrounded by the Ore Mountains Mining ores containing metals such as
cobalt had taken place in the region for centuries. The quality and value of the
ores varied immensely however. The cobalt ores ‘occur frequently
so blended with ores of silver that as one of the other metal must be
sacrificed it is often a matter of calculation to which works it will be
most advantageous to deliver them.’ So said Welsh industrialist John Vivien at
the meeting of the Royal Geological Society of Cornwall in February 1814.
Even so during the 18th and 19th centuries the manufacture and marketing
of smalt prospered in Saxony. In 1753 William Cookworthy, an enterprising
English pharmacist and porcelain manufacturer, acquired the exclusive
rights to the smalt produced at the Royal Saxon Cobalt Works in Schneeberg, a
town in Saxony. Over the following twenty years or so he shipped the material to
Bristol. It gave an attractive blue glaze to the white porcelain his factories
produced. At the time Bristol was renowned for glass making
notably bottle and window glass. Much of the glass was exported to the American
colonies. One of the most famous glassmaking firms was run by
father-and-son team Lazarus and Isaac Jacobs. Lazarus was born in Frankfurt,
Germany in 1709 and emigrated to Bristol around 1760. In 1774, Lazarus, an
expert glass cutter, and the 17-year old Isaac established a firm to manufacture
glass products. By the 1780s they were manufacturing high quality glassware stained blue using Cookworthy’s imported smalt. Bristol blue glass as it
became known soon became popular and can still be seen today in stained glass
windows and a variety of commercial products. Harvey’s Bristol Cream sherry,
for example, has been sold in distinctive Bristol blue glass bottles since the
1990s. Chemistry students may recall using cobalt blue glass in flame tests
to filter out the bright yellow light of the sodium flame. The use of smalt on ceramics can be
traced back much further to about 1500BC when it was used as a blue glaze for
Egyptian pottery. It was also used as a pigment to make Chinese blue and white
porcelain from the 13th century onwards Cobalt oxide was not used just to make
blue pigments. ‘Oxide of cobalt forms a green colour when heated with oxide of
zinc but as this compound is expensive it is not in use,’ Overman pointed out in
his book. That did not remain true for long however. Zinc oxide began to be
manufactured throughout Europe in the 1850s and by 1860 the cobalt green
pigment had become widely available. In his book on the chemistry of painting
and paints published in 1901 British chemist and artist
Arthur Church described cobalt green as ‘chemically and artistically perfect.’ Cobalt ores are usually found mixed with
other metal ores notably those of nickel and copper. Cobalt oxide and cobalt metal
are therefore usually produced as byproducts of nickel and copper mining
operations. The cobalt oxide used to make smalt and cobalt green is prepared from
ores that invariably contain other elements. Cobaltite for example is made
of a cobalt, arsenic, and sulfur and it is arsenic-containing ores that brings us
back to Overman. He emigrated from Germany to the United States in 1842 and
died of arsenic poisoning in Philadelphia in January 1852, the year
that his book was published He was just 49 years old. That was Mike fremantle with cobalt
oxide. Next week Brian Clegg twists his tongue around
terephthalic acid. That clumsy-looking name with the phth in the middle is a combination of two components There’s terebic, meaning derived from turpentine,
and then there’s ‘phthalic’, a contraction of ‘naphthalic’ from the petroleum-derived
hydrogen mix. And until then you can find all of our podcasts at Email [email protected] or tweet @chemistryworld with any ideas for compounds that we should include. I’m Ben
Valsler, thanks for joining me.

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