LIMELIGHT

Llanymynech in the limelight.

A little of the background to the limestone industry.

Why ‘LIMELIGHT’ ?

Llany Village HAll

To be ‘in the limelight’ means that someone is the centre of attention. This phrase is thought to date back to the days when the theatre or music-hall stage was lit by gaslight. The gaslight made everyone look very pale and unhealthy. When lumps of limestone were put in the gas flame a more flattering yellow-green light was given off. Hence someone who was on the stage was ‘in the limelight’.

Metals and minerals.
There has been a long history of gaining metals from the Llanymynech area, including the potential contribution to a king’s ransom. The main industrial heritage lies in quarrying and processing of limestone.

How did the limestone get here?

White clifs Dover

Geology tells us that the main part of limestone rock is the remains of the shells of sea creatures which lived millions of years ago. As the creatures died, their shelly remains collected on the sea bed. These remains built up and became ‘squashed’, to varying amounts, by other rocks forming on top. This resulted in the limestone rocks of different hardness. Chalk is the softest, as seen in the White Cliffs of Dover. Harder limestone has traditionally been used for building, St. Paul’s cathedral and the Cenotaph in London are made of this stone. Marble is the hardest form of limestone as this rock has also been affected by the Earth’s ‘volcanic’ heat as well as the pressure from other rocks.

Yes, this means that the land around Llanymynech was, a very long, long time ago, under the sea. More mind-boggling is that this land was near to the equator. The movement of the land masses on the surface of the earth and constant geological change resulted in the rocks which are with us today.

Why dig it up?

The reason that limestone has been quarried at Llanymynech since Roman times is not for the rock alone but what can be made from it. Not only is the rock useful as building stone but it is also used to make the mortar which binds the building stones together. Mortar is made by mixing gritty sand and [hydrated] lime with water. It is reported that when the Romans built the city of Wroxeter [photo below], they used mortar made from Llanymynech limestone. [The ‘lime mortar’ and stone of traditional buildings were replaced by cement and bricks from Victorian times onwards.]

1globe-thumb
Wroxeter

Limestone and its products have a range of uses from ‘fertilising’ the soil for better crops [liming the land] , making traditional paints [whitewash / limewash and distemper]  iron and steel [in a blast furnace], putty [mixed with linseed oil] and toothpaste! The main uses of Llanymynech limestone were in agricultures, building, making iron and steel and possibly lime-based ‘paints’.

Why all the kilns around Llanymynech?

The limestone rock itself has a limited range of uses. When it is heated to high temperatures, in all those kilns, it changes into a new substance. The limestone [known as calcium carbonate] becomes quick lime [calcium oxide]. To get the high temperatures, layers of limestone and coal are put into the kiln and the whole is ‘burned’. It’s really only the coal which burns and the heat produced changes the limestone to quicklime. The photo on the right is the part of a kiln where the lime and ash were raked out. There are several similar kilns in the area.

Kiln '2' by White House 2002

Quicklime gets its name from the old use of the word ‘quick’ to mean alive [as in ‘the quick and the dead’]. It seems to be alive when water is added to it. A cold lump of quicklime will swell, crack and get very hot when cold water is added to it. When all activity is finished a white powder remains which is called either hydrated lime [from ‘hydro’ - meaning water] or slaked lime [from ‘slake’ as in the old term to ‘slake’ or quench your thirst]. The chemical name of the white powder is calcium hydroxide.

As quick lime gets very hot when water gets to it then it causes heat burns and fires. Not only does it cause heat burns but it is very caustic or alkali and will ‘eat’ or ‘rot’ flesh.

If you were a canal barge owner taking on a load of quick lime from a kiln then you would have to make sure your boat was not leaking and also the cargo was protected from the rain. Otherwise………

In some cases the untreated limestone rock was taken away by barge and then ‘burned’ at a lime kiln some distance away, nearer to where the lime was used.

Lime kiln pub

This is why you can find canal-side limekilns and not a limestone quarry in sight.

Perhaps the quick lime was changed to hydrated lime before it was put on barges? It would certainly have been more safe. When the railways came to Llanymynech, taking the quicklime away must have not been as risky.

The coal for the kilns was brought in by canal. There was a relatively nearby coal mining area to the south of Oswestry in the Trefonen and Morda area. Some say that the Drill pub in Morda is named after the term in Welsh which describes a type of mine known as a drift mine. [Since this article was first written, the Drill has been rebranded as the Miners Arms]

The ‘burned’ lime which was raked out from the kilns must have been mixed with coal ash. Orders from customers sometimes asked for ‘the purest and whitest’ lime. It would be interesting to know how white the lime was with all the ash and cinders left from the burned coal.

Llanymynech limestone and agriculture

Lime [both quick lime or hydrated lime and also finely ground limestone] is used as a soil conditioner. When spread on the land it make the soil ‘sweet’ and is not really a plant fertilizer. When plants are grown for several seasons in the same ground, then the soil becomes acid or ‘sour’. Most food crops do not grow well in acid soil. As lime is an alkali, it kills or neutralises the acids in the soil when it is spread on the land. Lime has the added bonus of breaking down clay soils and releasing minerals which are needed for healthy crops.

blast furnace

Llanymynech limestone and the steel industry

Iron is made using very high temperatures in a blast furnace. The raw materials used in the furnace are iron ore, limestone and coal [or rather the coke made from coal]. The limestone from Llanymynech was used in the steel making communities of the Black Country such as Walsall and Wolverhampton. In the blast furnace the iron ore is changed to iron by the coke. The job of the limestone is to remove any earthy impurities in the iron ore. It does this by forming a liquid known as ‘slag’ which floats on top of the molten iron. When this slag is cooled down it forms a rock-like material.

Llanymynech limestone and the building industry

The slaked lime [produced by ‘burning’ the limestone, then adding water to the cooled product] was used for making traditional mortar. The slaked lime, a powdery material, is mixed with gritty sand and then water. This is all mixed well to form a ‘semi-solid’ mortar which can be worked with a trowel. The mortar is used to ‘bed’ the building stones together. These stones can be lots of different shapes or cut into rectangular blocks. The Cross Keys is a very good example of dressed or cut stone to the front of the building and ‘random’ stone to the rear.

Cross Keys

A bit of the chemistry of limestone

Limestone is mainly made of the chemical calcium carbonate. The three chemical elements of calcium, carbon and oxygen are chemically joined together to make calcium carbonate. The smallest, minute, sub-microscopic, ever-so-very-tiniest part or molecule of calcium carbonate has a formula CaCO[One atom of calcium, one of carbon and three of oxygen.]

When the limestone is heated in a kiln it breaks down to form calcium oxide [known as quicklime] and carbon dioxide is given off:

calcium carbonate [plus heat] --> calcium oxide + carbon dioxide
                     CaCO3 --> CaO + CO2

When water is added to calcium oxide it changes to calcium hydroxide [known as slaked lime] and a great deal of heat is given off:

calcium oxide + water -->calcium hydroxide [plus heat]
         CaO + H2O --> Ca[OH]2

When calcium hydroxide is left in contact with the air [and the water in the air] it joins up with the carbon dioxide in the air to make calcium carbonate.

calcium hydroxide + carbon dioxide --> calcium carbonate
                 Ca[OH]+ CO --> CaCO3

This making of calcium carbonate explains why mortar goes hard – but it takes a long time.

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Above article by Glyn Gaskill

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