Is alum good for eczema

Visitor mine

Cultural and technical history of alum works and mill wall

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Alum - tried and tested for thousands of years

Alums are double salts of sulfuric acid. There are several types of this, depending on the (cation) metals involved. Potassium aluminum alum - potash alum for short - has been the most valued since ancient times. It was accordingly highly traded and used in many ways, especially as an often indispensable aid for coloring. In the tomb of the ancient Egyptian king Tutankhamun (14th century BC), besides many treasures, there were also cloths dyed with madder, which must have been stained with alum beforehand. The ancient Greek author Herodotus (5th century BC) also mentions alum as a pickling agent.

You could also use it for eggs and cheese durablehe do and so z. B. 'save' through Lent. In the Healing art one used the alum to stop bleeding, for skin treatment for eczema, for gargling for mouth and throat diseases and even for contraception. The razor pens and deocrystals that are still commercially available today are mostly made of ammonium alum. Another application that is still practiced is the tanning of hides, which is also used in addition to potash alum for white tanning - from sheep, goat and small animal skins - the (environmentally harmful!) Chrome alum is also suitable, e.g. for shoe leather.

⊕ Alums and Vitriols - definition of terms | show ⇓

+ Alums and vitriols - definition of terms

As Alums denotes a group of salts of sulfuric acid. They are crystal water containing Double sulfates with monovalent and trivalent cation metals (or monovalent ammonium ion). So there are quite a number of alums, the most famous of which are:

  • the potassium aluminum sulfate, for short Potash alum, often with alum meant;
  • Ammonium aluminum sulfate: ammonium alum; used in cosmetics (deodorant, razor stick);
  • Potassium Chromium Sulphate: colored chrome alum, suitable for tanning;
  • Iron-aluminum sulfate: iron alum that is made up of it Federalaun, the Mineral halotrichite (see menu item natural monument);

The sum formula of the most important representative potash alum is:
Potassium aluminum sulfate (dodecahydrate) = K2SO4 * Al2(SO4)3 * 24 HOURS2O
The potash alum forms beautiful, octahedral crystals. Octahedra are geometric bodies that ideally consist of eight surfaces of the same size (triangles).

One often comes across the term in connection with historical alum works vitriol. It refers to Simple sulfates divalent (cation) metals. Mostly one meant the iron vitriol or iron (II) sulfate (FeSO)4).

All of these exact definitions are of course recent and are not historical. In the past, one differentiated the salts only according to their external properties. Alum and vitriol were often obtained together. Often the smelters could not determine which amount of which salt came out of their work. They still lacked the chemical background knowledge to master the processes. The different compositions of alums were also unknown to them, they just knew different qualities and uses. As far as we know today, potash alum was considered good alum, it was up to 10 times more expensive than vitriol. In this respect one was particularly successful in Mühlwand, although the original concession was also on "Alum, Vitriol and Sulfur Waser" read; more on this below.


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The alum works of the Middle Ages and the Renaissance

People have been producing since ancient times Alum off the mineral Alunit, the alum stone, a type of alum hydroxide. Mining was in Phocea and on some islands in the Byzantine Empire (now Turkey). From there, alum was supplied to all of Europe. When the Ottomans (Turks) conquered Constantinople under Mehmed II in 1453, the continent was cut off from deposits. From now on, alum has to be bought dearly from the 'enemies of Christianity'. Pope Pius II, Enea Silvio Piccolomini (1405-1464), prayed for a miracle ... and it happened - at least in the eyes of the Pope. In 1462 Giovanno di Castro discovered large deposits of alunite near Tolfa in the Papal States and the Vatican founded a large alum plant.

Pius II immediately secured the monopoly on the alum trade for the Vatican. In his Easter bull of 1463 he forbids all believers to buy alum from the enemies of Christianity. He threatens apostates with excommunication. With the proceeds of his large alum factory - it employed up to 6,000 workers in some cases - Pius II also wants to finance a crusade against the Turks.

"Today I bring you the victory over the Turks, because they extract more than 300,000 ducats from Christendom annually for their alum needs."

However, he died as early as 1464 while putting together a force in Ancona.


In the meantime one had in Europe learned Alum also made from black slate to win, albeit with varying degrees of success. The first alum work of the Renaissance was made in Bohemia in 1497. In the 16th century - not least due to the Reformation from the danger of being banned from the church - such works were created in many European countries, including in the Vogtland for a short time near Plauen (1542-1547, Schurig) and Neumark, (1558/1559 Börner). However, the quality of their products was often complained about because it did not come close to the - still coveted - Turkish alum. Without the chemical knowledge of the composition of the substances and their transformations, the process was not really mastered.

⊕ Alum extraction from alunite (alum stone) | show ⇓

+ Alum extraction from alunite (alum stone)

The sequence of images shows the extraction of Alum from alum stoneas it was practiced in the Orient and later in Tolfa (Italy) (however not in Mühlwand). Typically, the mineral is burned in a shaft furnace. The Saxon mining expert Georgius Agricola (* March 24th, 1494 in Glauchau; † November 21st, 1555 in Chemnitz) noticed the similarity with lime burning. He had intuitively recognized the decisive process: the dehydration of the stone to sulfate, even if he could not yet know anything about the chemical processes.

In the alum works of the Renaissance, the Slate instead of alum stone processed, that couldn't work. To do this, the crushed slate was left damp for several years, often mixed with putrid urine or animal waste. The pyrite contained oxidized in the air to form sulfuric acid, which combined with metal cations from the slate or the ammonium from urine to form salts. Whether in the end 'good or inferior' alum, potash or other alum, or even just vitriol, was a matter of luck (see also below The 'secret' of the roasting stage ').

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The historic alum factory in Mühlwand

June 9th 1691 mining captain Abraham von Schönburg gave the Reichenbacher Bergmeister Paul Döring the electoral "... Concession on the establishment of a vitriol, alum and sulfur-water plant around the same area". Quick was a Quarry developed and Tunnels and shafts Drifted underground far beyond the property boundaries. One set up on the Göltzsch Hut House as well as a Boiling hut.
Despite repeated setbacks due to ingress of water and neighborhood disputes around a dozen men a year a few hundred hundredweight best potash alum. Customers were next to Tanning and dyeing works also the Reichenbacher Clothierto whose guild the alum factory initially belonged - as well as the dye works and fulling mills in the area. But despite the flourishing business and the tithe estate, the proceeds remained modest, also because the prices were fixed. Soon production was only based on wear and tear and the systems fell into disrepair.

⊕ The Mühlwander alum boiling | show ⇓

+ The Mühlwander alum boiling

A particularly effective alum boiling process is practiced in Mühlwand. The miners dug the alum shale in tunnels and openings with mallets and irons, but also hand drills and black powder. Cart runners then carried him to the fireplace, where the burners chopped him up alternately with firewood to make an outside sealed with earth lying pile piled up that one Roasting stage called. This was set on fire and its burn through was controlled very precisely: stimulated by stoking, steamed by pouring water over it (in a double sense!). The base sulfates required for alum were formed during this process (see: 'Secret' of the roasting stages). This could take up to four weeks and produced mighty, acrid clouds of smoke.

Often several roasting stages were in operation at the same time. Then the slate quarry was an impressive sight. The Greizer Hofrat Struwe describes it in 1806 as
"... large, deeply carved fracture ... which, because of its dark black color and the high heaps piled up on both sides of the path, resembles the workshop of a volcano; the widespread sulfur vapor and the thick steam rising from the burnt alum ores increase the illusion and contrasts strangely with the fir forest that surrounds it. "

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After it had burned out, the kiln was pulled apart, the incineration slag shoveled into the wooden basin of the Laugplatz and mixed with the water from a brook running through the area. In the map from 1787 shown, you can see whole rows of such boxes. The sulphates, which are important for alum, were released from the slag while stirring vigorously. Then the salty water - a greenish "leek" - was allowed to run off and flow through an almost 200 meter long wooden pipe to the boiling hut on the Göltzsch. At first it should have looked similar to the woodcut (picture on the right), but with three separate boiling pans and several boxes.

Alum factory Mühlwand
from right to left:
  • Slate mining,
  • Burning in roasting stages,
  • Rinse in 'lye boxes',
  • Evaporation in the brewhouse,
  • Alum crystallizes on cooling.

The washed-out slag, now brick-like to purple-red because of the remaining iron oxide, was piled sideways to form large heaps. In the hut, the salty solution was allowed to evaporate in the heated lead pans, which kept increasing the salt concentration. The need for firewood was considerable and the pans were worn out. Around 1799, what was then an ultra-modern two-pass boiling complex with two brewing and three preheating basins was built, walled on all sides with flue gas flues for the best possible use of the heating energy.

In contrast to the boiling of table salt, the sulphate brine was not allowed to evaporate completely, but from a certain concentration - the boiling master checked it with a small hand pan - it was poured into special ones while it was still hot Cooling basin. Grates made of bars or strings weighted down with stones were hung from above. When the alum cooled, the alum attached itself to them in the form of often large octahedral crystals. They were then taken off in the defeat dried and weighed and packed in kegs for dispatch.
In this way, around a dozen men annually produced around 400 quintals of the best potash alum - in addition to a few hundredweight of vitriol.

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The owners, tenants or foremen often changed. The plant came to a complete standstill several times, including during the Seven Years' War (1756 - 1763), when it was occupied and damaged by the Prussian military. Not least because of its importance for the cloth-making town of Reichenbach, the electoral chamber (state) took over the plant in 1765 and invested in extensions and one new boiling hut. Around 1800 they dug a deeper drainage tunnel and opened up another sole. In the brewhouse on the Gölzsch one was remarkable modern boiling plant built. But already 1827 the factory was finally closed. Mühlwand could not compete with alum, which was now chemically produced. As if by a miracle, the last roasting stage was preserved. The slate rubble, piled up too high, was then used as building material, for example when the Göltzschtal viaduct was built four kilometers down the river, which is still the largest brick bridge in the world today.

One often hears that Mühlwander alum was used for the construction of the Göltzschtal bridge (1846 - 1851). In fact, the burnt-out slate remnants lying on the dump were initially used. They were ground and mixed with the masonry lime, which gave the mortar the ability to harden even in the absence of air and even under water (hence called "hydraulic" mortar). Such a hydraulic mortar was very important for the meter-thick pillars of the bridge: they had to harden quickly in the core - i.e. without air admission - in order to be able to bear the weight of the rising structure in good time. Cement had already been invented, but it was still far too expensive for the great needs of the bridge. The slate fire residues, on the other hand, ideally consisted of the three - as we say today - "hydraulic factors" clay (aluminum oxide), quartz (silicon dioxide) and iron oxide (the burning residue of pyrite).

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⊕ The 'secret' of the roasting stage | show ⇓

+ The 'secret' of the roasting stage

In order to appreciate the achievements of the alum workers in Mühlwand, you have to know that nobody had any real chemical knowledge at that time. The foundations for this were only just being researched: around 1772, Scheele and Priestley discovered oxygen, and chemical conversions through oxidation and reduction were first described by Lavoisier in 1783. This did not affect practice until much later.

One thing was clear: no salts could be extracted from freshly hewn slate. However, it was observed that the longer the broken rock was stored outdoors, the better the yield. The alchemists explained this quite strangely with the power of the stars, their influence and the "Union of the male principle of the sun and the female principle of the moon". In many places, therefore, leach platforms were set up on which the slate was stored outdoors for years and occasionally doused with rotten urine. After all, iron vitriol or the less popular type of alum ammonium-iron could form in the process. They could also be sold, but only the potassium-aluminum-alum was considered the "best alum". The Mühlwander plant achieved an almost 100% yield of this, which is why it was one of the most successful of its time. The reason for this lies in the consistently consistent method of burning slate in roasting stages.

Roasting stages are rather flat, "lying" piles that rise at an angle to the rear. They were placed in layers from crushed (moist?) Slate and firewood and sealed on the outside with earth. They were then lit at one end and allowed to burn through in a precisely controlled manner.

At Raw materialsn for 'best alum' (Potassium aluminum sulfate) were already present in the slate: aluminum in claystone and sulfur in the form of pyrite. He also stepped with the combustion air oxygen added. And with the firewood - specifically its ashes - also got there potassium (Potash = potassium carbonate) into the "chemical reactor" that the roasting stage actually represented. That was their first "secret of success".

But how the substances are implemented in detail is the second and real secret of the roasting stage - to this day. The fire of the wood and the carbon in the slate "roasted" the pyrite first, whereby itself Sulfur oxides must have formed. They combined with moisture too sulfuric acidwhich, as a strong acid, dissolved the potassium and aluminum from their compounds and attracted them. So far so good. But it must have 'somehow' happened gradually and in differently hot, ventilated and also humid areas. Without any knowledge of chemistry, the burners could only master the process on the basis of long experience, through careful stoking, watering and sealing.

In the residues of the last Mühlwander roasting platform, you can find pieces of annealed and caked clay slate with red coatings that look as if they had been excreted from a liquid. It is likely that iron sulphate was first formed from the oxidized pyrite, which was then more or less fluidly 'roasted' again on the pottery shards. It left behind a red, purple tinge Iron oxide-Pigment, a typical end product of vitriol burning that the alchemists once used caput mortuum - skull - called. By that they meant its peculiarity as an immutable, quasi-dead remnant. The iron was now eliminated from the conversion processes in this insoluble form. Bound to the slag, it could no longer disturb the formation of potassium alum. In contrast, it now worked as catalyst the necessary conversion of the sulfur oxide from SO2 to so3.

All in all, the 'roasting' of the alum ores was a very complex chemical process, not nearly comparable to charcoal or lime burning. In this respect, the term "chemical reactor" for a Mühlwander roasting stage is not exaggerated - but a reactor that was found and operated purely intuitively and that has kept its last secret to this day.

Last but not least, its location on the Göltzsch was an advantage for the metallurgical success of the Mühlwander alum plant. This enabled it to be adequately supplied with wood, an important source of potassium and energy. At that time, logs were floated from the Vogtland forests to Leipzig and the salt pans of Halle. The Mühlwander factory had the privilege to produce 300 fathoms (approx. 1000 m3) refer to.

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Mill wall in the 19th century

As early as 1703, the tenants of the alum plant had been buying beer to refresh the workers while they were working in the boiling ovens. In 1714, resentful Reichenbacher brewers complained because beer was also served to passers-by - but especially Mylauer beer! The tenant had to pay a fine of 20 Thaler, but was now allowed to operate the bar legally. This established a long serving tradition in Mühlwand, which far outlasted the active time of the mine. At the location of the hat house on the Egerschen Brücke - the Göltzsch crossing of the important Reich and trade route from Leipzig and Dresden to Nuremberg and Eger - there was always a lot of traffic. After a dangerous downhill and then uphill drive, the carters gladly took advantage of the opportunity to rest and relax. In addition, the Saxon post office at the Huthaus kept harness horses ready for heavy wagons, which had to be rented for certain wagon sizes in order to avoid accidents.

In 1827 the boiler with its round boiler on massive iron beams was dismantled, which produced 100 quintals of iron and lead - today it would be an imposing technical monument for Saxony. Hut and Siedehaus continued to exist as the inn "To the Three Swans". In the old mine area, the landlord built a beer garden with a bandstand and bowling alley. On mild summer days he organized "Italian Nights" with dancing under lantern light, to which guests flocked from far away. But in 1853 the inn burned down, but it was quickly replaced by a new inn "Zum Alaunwerk" (demolished in 2004). The Mylau-Lengenfeld railway line, which opened in 1905, brought Mühlwand again numerous guests and visitors to the 'summer freshness'.

On the way to the visitor mine

In 1928 the teacher Leander Macht from Greiz first pointed out the possibility that a similar attraction could be hidden in Mühlwand as the one in the Saalfeld fairy grottoes. But it was not until 1954 that a flood exposed some of the closed tunnel entrances and flushed out sintered formations. Friends of home began to explore the mine. They exposed entrances and made a separate stalactite grotto accessible to visitors. But the planned construction of a dam with a dam at Rotschau thwarted further efforts from the 1960s onwards. The backwater would have flooded the Mühlwand and the mine. The entrances were closed again and - almost - forgotten.

After the fall of the Berlin Wall, friends of home again got involved in the alum factory, explored and cleared the area and redesigned the outdoor area with paths and benches for visitors. In 1995 the old entrances were tracked down again and came across a grotto with magnificent stalactites. The development association, founded in 1998, was named after her and laboriously cleared the silted tunnels and shafts. Unfortunately, for technical reasons it was not possible to make it accessible to visitors. The mine itself, on the other hand, could be developed in other equally worth seeing areas over a length of around 500 meters. Access to the entire underground facility is neither possible nor sensible anyway - with a total length of up to 10 km, as one suspects.

In September 2001 the time had come: the mine symbolically opened its tunnel door to the public and has been well attended ever since. However, the floods of 2013 brought with it a - fortunately temporary - interruption of visitor operations. Guided tours have been taking place in Mühlwand again since 2018.

⊕ The flood event of 2013 | show ⇓

+ The flood event of 2013

The floods of 2013 meant a severe setback for visitors. Heavy rainfalls for days had caused the otherwise small rivulets from the adjacent forest canyons to swell up. The masses of water devastated the area, flushed out heaps and paths, looking for the way into the mine laden with rubble and mud. For the visitor business it meant the temporary end - for the adjoining residential properties and streets, however, the rescue.

In order to protect these from similar floods in the future, a dam was built in the area for rubble and parts of the mine were expanded specifically for the safe discharge of floods. Critical tunnel sections are secured with shotcrete and steel elements, but otherwise the mine building was left in its historical dimensions. The modern extensions do not disturb the attractiveness of the facility, on the contrary, they offer the visitor additional interesting views.

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