Historically, potassium alum was used extensively in the wool industry from
Classical antiquity, during the
Middle Ages, and well into 19th century as a
mordant or dye fixative in the process of turning wool into
dyed
bolts of cloth.
Antiquity Egypt Potassium alum was also known to the
Ancient Egyptians, who obtained it from
evaporites in the Western desert and reportedly used it as early as 1500 BCE to reduce the visible cloudiness (
turbidity) in the water.
Mesopotamia According to the expert on Middle Eastern history of chemistry Martin Levey, potassium alum is one of the few compounds known to the ancients that can be found relatively pure in nature, as well as one of only a few chemicals used in
Mesopotamian chemical technology that can be identified with certainty. Both native and imported potassium alum was used. This site was abandoned in the 7th century but dates back at least to the 2nd century CE.
Rome Potassium alum was described under the name
alumen or
salsugoterrae by
Pliny, and it is clearly the same as the
stypteria (στυπτηρία) described by
Dioscorides. However, the name
alum and other names applied to this substance — like
misy,
sory,
chalcanthum, and
atramentum sutorium — were often applied to other products with vaguely similar properties or uses, such as
iron sulfate or "green vitriol".
India and China Potassium alum is mentioned in Ayurvedic texts namely Charak Samhita, Sushurta Samhita, and Ashtanga Hridaya with the name such as
sphaṭika kṣāra,
phitkari or
saurashtri. It is used in
traditional Chinese medicine with the name
mingfan .
Middle Ages In the 13th and 14th centuries, alum (from alunite) was a major import from
Phocaea (
Gulf of Smyrna in Byzantium) by Genoans and Venetians (and was a cause of war between
Genoa and
Venice) and later by
Florence. After the fall of
Constantinople, alunite (the source of alum) was discovered at
Tolfa in the Papal States (1461). The textile dyeing industry in
Bruges, and many locations in Italy, and later in England, required alum to stabilize the dyes onto the fabric (make the dyes "fast") and also to brighten the colors.
Modern era England Potassium alum was imported into England mainly from the
Middle East, and, from the late 15th century onwards, the
Papal States for hundreds of years. Its use there was as a
dye-fixer (
mordant) for
wool (which was one of England's primary industries, the value of which increased significantly if dyed). These sources were unreliable, however, and there was a push to develop a source in England especially as imports from the Papal States ceased following the
excommunication of
Henry VIII. With state financing, attempts were made throughout the 16th century, but without success until the early 17th century. An industry was founded in
Yorkshire to process the
shale, which contained the key ingredient,
aluminium sulfate, and made an important contribution to the
Industrial Revolution. One of the oldest historic sites for the production of alum from shale and
human urine are the Peak alum works in
Ravenscar, North Yorkshire. By the 18th century, the landscape of northeast Yorkshire had been devastated by this process, which involved constructing stacks of burning shale and fuelling them with firewood continuously for months. The rest of the production process consisted of quarrying, extraction, steeping of shale ash with seaweed in urine, boiling, evaporating, crystallisation, milling and loading into sacks for export. Quarrying ate into the cliffs of the area, the forests were felled for charcoal and the land polluted by sulfuric acid and ash.
Identification of the formula In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum. The error was soon corrected by
Johann Pott and
Andreas Marggraf, who showed that the
precipitate obtained when an alkali is poured into a
solution of alum, namely
alumina, is quite different from
lime and
chalk, and is one of the ingredients in common
clay. Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina in
sulfuric acid and adding
potash or
ammonia to the concentrated solution. In 1767,
Torbern Bergman observed the need for potassium or ammonium sulfates to convert
aluminium sulfate into alum, while sodium or calcium would not work. At the time, potassium ("potash") was believed to be exclusively found on plants. However, in 1797,
Martin Klaproth discovered the presence of potassium in the minerals
leucite and
lepidolite.
Louis Vauquelin then conjectured that potassium was likewise an ingredient in many other
minerals. Given Marggraf and Bergman's experiments, he suspected that this alkali constituted an essential ingredient of natural alum. In 1797 he published a dissertation demonstrating that alum is a
double salt, composed of sulfuric acid, alumina, and potash. In the same journal volume,
Jean-Antoine Chaptal published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum and alum manufactured by himself, confirming Vauquelin's results. ==Characteristics==