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What were alum and vitriol used for?
For centuries, the “Buckelapotheker” (itinerant pharmacists) shaped the trade in natural remedies in the Thuringian Forest. Carrying medicinal herbs, ointments, and tinctures—known as “Olitäten”—they traveled on foot through large parts of Europe, spreading the knowledge of local herbalists far beyond the region. Alum played a special role in this—a versatile mineral used in medicine, papermaking, leather processing, and textile dyeing, among other things.
Alum – Mode of Action and Use
Alum is a double salt of sulfur. Until 100 years ago, it could be found in almost every household and was used in many trades: in tanning, medicine, as a wood preservative, in paint production, sizing, pickling, bleaching, and preserving.
Potassium aluminum alum, or potash alum for short, was particularly versatile because, unlike iron or chrome alum, it does not lead to discoloration in important applications.
Potash alum dissociates completely in aqueous solution into potassium, aluminum, and sulfate ions.
K2Al2(SO4)4 + 8H2O <—-> 2K+ + 2AL3+ + 8(OH)– + 8H+ + 4SO42-
Both the aluminum and sulfate ions were of practical importance. Before sulfuric acid could be produced on an industrial scale, alum was the most important source of sulfate ions. In a sense, an aqueous alum solution represents a temporary sulfuric acid, which explains its astringent property—that is, its contracting and solidifying effect on proteins. Furthermore, sulfate ions oxidize some non-fast dyes, converting them into colorless forms, which results in bleaching. Finally, sulfate ions have bactericidal and germ-inhibiting effects. These three properties overlapped in individual applications.
The Buckelapotheker
As early as the Middle Ages, traveling merchants were called “Buckelkrämer” (back-peddlers) because they always carried their wares with them on their backs (“Buckel”) using a wooden frame known as a “Reff,” moving from place to place.
For centuries, herbalists in the Thuringian Forest collected native medicinal plants and processed them into remedies known as “Olitäten” (from the Latin oleum – oil).
At that time, anything used by the common people as a natural remedy was referred to as an “Olität,” either because they could not afford medical assistance or because doctors did not want to prescribe such remedies as aloe or opium.
Packed in clay jars, glass bottles, and chipboard boxes, the ointments, herbal preparations, and tinctures—as well as alum crystals from the “Jeremias Glück” mine—were carried out into the world by the back-peddlers.
From the Thirty Years’ War until the 20th century, they transported the goods on foot during journeys lasting several weeks. They sold them primarily to the princely and royal houses of Europe. Individual families were responsible for specific sales territories and were thus able to establish a kind of monopoly.
In 1780 alone, about 800 itinerant pharmacists were on the road between Denmark and Hungary, as well as Poland and France. The products were also shipped overseas via Dutch ports.
Although laws were passed in some German regions against hawkers and thus also against itinerant pharmacists—even prohibiting the accommodation of back-peddlers—the trade in Olitäten reached its peak in Thuringia in the 18th century.
Dressed in a brown tricorn hat, brown frock coat, red vest, white neckerchief, brown leather trousers, and gaiters, they were no longer called “masterless rabble” but “God-praised laboratory assistants from Thuringia.” They enjoyed high prestige, and even doctors and surgeons valued and followed their advice. They were thus the forerunners of representatives of the spirits and pharmaceutical industries.
After the Second World War, the distribution lines could no longer be maintained. Many family members of the itinerant pharmacy dynasties found work as employees of the VEB Pharmazeutisch-Chemische Fabrik Meuselbach, today’s Krewel Meuselbach GmbH.
Medicine
In the medicine of former times, alum was considered a true miracle cure. The powder was used against all kinds of inflammation, eczema, and weeping rashes, but also for contraception—sometimes simply by carrying it in a small cloth bag.
It was even said to help against anxiety and feelings of guilt, and in the Orient, alunite serves as a protective stone against possession and enchantment.
In 1679, Lonicerus recommended mixing the powder with earthworms and grinding it well to obtain an ointment against cancerous ulcers. In addition, alum was said to help against itching, scabs, fistulas, “putrid flesh in wounds,” as well as lice and nits.
Alum has an astringent and disinfecting effect. For this reason, it can be used to stop bleeding and to treat hemorrhoids in alum baths. Due to its antibacterial effect, it was used as a deodorant as early as Roman times. Applications against sweaty hands and feet, sluggish blood flow, long-lasting mucus discharge, diarrhea, and lead colic are well known.
Textile Dyeing and Paint Production
Dyers use the mordant effect of alum to be able to dye textile fabrics permanently. When mordanting and dyeing textile fibers, the aluminum ions act as a chemical mediator between the natural fiber and the dyes by forming complex compounds.
Fabrics are boiled in alum solution before being soaked with aqueous extracts from dye plants.
The Romans already dyed fabrics in this way to produce the typical bright toga.
Madder root, dyer’s madder, and logwood served as dye plants.
In the production of paints from natural plants, alum is used to mix color pigments with a binder. In an aqueous solution with potash and caustic soda, alum transforms into the finest white alumina crystals to which natural pigments bind. This produces spreadable pigment masses for artist’s paints and gouache.
Papermaking
Until the 19th century, paper was made from rags and fiber plants. During this time, alum served to bleach and strengthen these paper components.
With the invention of the groundwood process by J. C. Schiffer in 1765, the foundation for the mass production of paper from wood cellulose was laid. Untreated, this paper acts like blotting paper and is unsuitable for writing or printing.
Water-repellent alum is added to the cellulose paper with abietic resin soap to prevent the ink from running. However, the sulfate ions introduced by this process lead to the so-called “death of books” because the paper acid causes books and documents in archives to disintegrate.
Fire Retardant, Extinguishing Agent, and Weathering Protection
Findings from Egypt prove that wood was already being impregnated with alum as a flame retardant around 450 BC. The Romans also used it mixed with vinegar for this purpose.
In the Middle Ages, wooden roof structures and fortifications were treated with alum salts to protect against weathering and animal pest infestation, but above all as a preventive fire protection. Armorers also soaked wooden weapon parts with alum to make them more fire-resistant.
Extinguishing powders with the addition of alum were in use in the 18th century, and as early as 83 BC, fires were extinguished with alum solutions.
Alum provides a limited flame retardancy because its relatively high proportion of water of crystallization is released when heated and inhibits the ignition of the wood: wood treated with alum becomes moist when heated!
Tawyer (White Tanner)
In the making of the leather /
the stench is the main feather. /
Lime, alum, salt, flour, arsenic, /
make it white and quite the trick. /
Egg yolk, punkel, doggy poo /
give it special quality too. /
Thus it is a pure delight /
to kiss a glove so soft and bright.
This tanner’s rhyme describes the auxiliary materials necessary for tawing or alum tanning.
Tanning is carried out using minerals such as alum and common salt and produces a light, almost white tanned leather – hence the name tawing (white tanning). Tawing is mainly used for finer, thin leathers from calf, sheep, and goat. After cleaning the skins of blood, meat, and fat residues, the tanners rub moist alum into the washed-out hide in this very old process. This causes the protein fibers to contract, cross-link, and solidify.
Once dried, the leather is stiff and hard and must be made supple through mechanical processing, greasing, and dyeing. The tanning is not permanent and can be washed out again.
Viticulture and Agriculture
Alum and its by-products are used in agriculture and specifically in viticulture.
Aphids and caterpillars on berry bushes are killed by pouring a hot alum solution over them. Alum is also used in viticulture against phylloxera. Copper vitriol in particular, which is formed when sulfuric acid washed out of the alum shale meets copper, is a sought-after agent for combating phylloxera.
To prevent rust (white vitriol) in wheat, it is sprinkled with copper vitriol.
In the 19th century, the demand for copper vitriol far exceeded the supply in some years, while in others it was exported in large quantities.
By adding alum to the watering water, the flower umbels of hydrangeas bloom in a blue or violet color.