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Glenbuchat Heritage

7 Part 6 Kilns: Limekilns and Lime Burning
The Glenbuchat Image Library
7 Part 6 Kilns: Limekilns and Lime Burning

Pictures above
1. Limekiln at Badenyon
2. Diagram of Kiln Construction
3. Unknown 19th Century kiln Glenbuchat
4. Large Draw hole in kiln
5. Stepped lintels

Click for the Introduction page

Limekilns and Lime Burning

Early kilns

Early limestone burning in North East Scotland involved the use of simple ‘clump’ (or clamp, or common, or sow) kilns. At a time before good estate roads were laid down in the late 18th and early 19th centuries and the general use of carts adopted, peat was carried on horseback from the nearest peat moss to the clump kilns sited next to the quarry excavations. Burning the limestone at the quarry reduced the weight of material to be transported to the fields, as the burnt lime (quick lime) weighed around half that of the original limestone rock.
Surprisingly, clump kilns were used in some areas of the North East long after the general introduction of the more efficient ‘draw kilns‘, as this account of a small commercial quarrying operation from the parish of Old Deer, Aberdeenshire, in the 1840’s describes:
‘The stone, detached from the rock by iron crows (crow bars, large hammers, and blasts of gunpowder is broken by smaller hammers into fragments, as if intended for the substratum of a turnpike road, and calcined in small clump kilns with peats.’

In clump kilns, the shattered limestone pieces and peat were built up in alternate layers and covered with stone or turf to form a mound, with air vents left to the interior for ventilation:
‘The limestone is mostly burned in clamp or saw kilns, improved as much as possible by air pens, carried up the sides and ends, and stacked with brushwood.’

However, they had a low and uncertain output of burnt lime. Uneven distribution of heat within the kiln meant both under-heating which left the limestone largely unconverted, and over-heating which fused it, within the same firing. As a result, an extra and unpleasant process had to be carried out on the caustic burned lime:

‘The heterogeneous substances which the fire had not decomposed, or fused slug caused by the excess of heat, are separated from the dust by a riddle or sieve wrought by hand’

The kilns were broken open to remove the lumps of burnt limestone, and could be re-used with careful rebuilding. Being temporary structures, they have probably long since disappeared local, but remains of large clump kilns have survived in the Lothians and Borders. More permanent clump kilns took the form of long shallow pits dug into gentle hill slopes, and groups of these have been found next to quarries in areas of central Scotland, but so far, no surviving examples have been identified in the Upper Donside area.

Draw Kilns

The big step forward in local lime production came in the late 18th and early 19th centuries with the adoption of the more efficient, higher-output stone-built draw kilns.(picture 3) Improvement of local estate roads and the use of carts meant that it was now practical for farmers to cart peat and limestone in large quantities to kilns built on their farms and crofts, next to the fields where the lime was to be used. The siting of a particular limekiln depended on local topography. It was invariably set into a natural bank with access for a horse and cart by a gently sloping track to a loading platform at the rear, and with access to the front of the kiln for raking and shovelling out the burnt lime from the draw hole. (Some areas of Britain report kilns built with their draw holes aligned to the prevailing winds to improve the burning process but there appears to be no pattern of this in Upper Donside). An additional consideration was a nearby supply of water to slake the burnt lime before it was spread on the land, and many of the limekilns were sited on the banks of a burn.

The more sophisticated design of these permanent, circular stone structures gave a huge advance in lime production when compared with the primitive clump kiln. Their main feature was the large draw hole on the front face of the kiln. (picture 4) Air was funnelled by a series of inverted, stepped lintels (picture 5) through a small opening at the back of the draw hole to the interior bowl-shaped 'pot', containing the alternately layered peat and limestone (Illus. 22).The inverted stepped lintels, varying in number from 2 to 6, depending on the height of the kiln, supported the weight of the pot while giving access from the draw hole to the opening at its base for the supply of ventilation and for emptying it. *

(*No digging was attempted and it was assumed that there was an opening (flue)at the back of the draw hole connected to the interior to allow air to enter the pot, and for emptying of the kiln of burnt lime. Otherwise, a man would have had to enter the kiln from the top and carry the caustic lumps of burnt lime out of the bowl using ladders and baskets and ropes.)

It was important in the design and construction of the limekilns that the only entry for air was through the draw hole. While the exterior of the kiln was typically built with large fieldstones, the interior walls of the pot were lined with smaller, close-packed stones (with no sign of lime mortar used). Small stones were in-filled between these two courses of stone-work. The air-tight walls of the kiln meant that higher kiln temperatures were achieved. and the burning process could be more easily controlled, giving a more even and complete burn of the limestone. The thick stone walls conserved heat within the pot and their sturdy construction meant that it could be re-used time and again.

‘Burning’ Limestone.

The farm limekilns of the area were operated as ‘intermittent kilns’, worked on a cycle of loading, firing, cooling and emptying. (‘Continuous kilns’ were run on a more efficient industrial process. kept burning constantly by loading fuel and limestone from the top and raking out the burnt lime at the base from beneath a grate. There is no evidence of this type of kiln in the area.) Simply tipping peat and limestone into the bowl haphazardly was not an option. Loading, (or charging), the limekiln was a skilled labour-intensive operation, done by hand. Quarried limestone rock was broken into pieces, approximately the size of half a brick or less, by hammer and stacked in the bowl with alternate layers of peat. The use of dry peat was important for the kiln to reach the high temperatures required in the burning process. The first layer was of wood or brushwood, to kindle the peat and the aim was to provide for a well-packed kiln with good ventilation, which would burn at a sufficiently high temperature for the conversion of the limestone to burnt lime. Once the kiln was loaded, a fire was kindled at the back of the draw hole. As the peat began to burn, the updraft of hot gases would draw air into the pot through the draw hole, and the kiln would be firing. This was a critical time: run too fast and hot, the limestone would fuse and leave other areas unconverted. Run too cool, the limestone would fail to ‘burn', with the danger of the kiln going out. The temperature and rate of burn up the height of the bowl were controlled by a damping-down procedure, apparently by covering the top of the kiln with turf. As described in an account of charging and firing a small limekiln from the early 19th century:

‘One man is sufficient within the kiln. The bottom of the kiln is to be covered with o layer of peat about 9 inches thick, over which another layer of (lime ) stones not quite three inches thick is placed, and so alternately till the kiln is filled. Towards the tap, the layers may be gradually thickened, that of limestone to four inches and that of peat to twelve inches. The last layer should be a thin one of peat covered with thin turf. If the turf were dry, a few baskets-full of crumbled peat will be sufficient for the upper layer. Between the layer of limestone and the sides of the kiln, a row of peats should be inserted, (so) that the edge of the layer may not be burnt partially. To prevent the limestone from falling down between the interstices of the pears, the top of the peat layer should be covered with crumbled peat’.

‘During the burning of the lime, if the wind blows, a man should attend to cover the kiln with turfs, where the flame breaks out, in order that the contents may be equally burnt’ ‘As both peats and limestone vary in quality (from district to district), the proportions of the two layers must be modified by this circumstance. The best limestone is most difficult to burn, and the best fuel for burning is the brittle black species?’


The above description gives an indication of the large amount of fuel required for the burning process. A ratio of around 4 or 5 cart-loads of peat to 1 of limestone was used. Given an estimated less than 50% return (by weight) of burnt lime from the original limestone rock, perhaps the equivalent of less than half a cart-load was produced. It can be seen that the yields of burnt lime per kiln firing were low.

Lime ‘burning’ involved heating the limestone to a temperature sufficient to convert the calcium carbonate of the mineral into its two oxides, calcium oxide and carbon dioxide. The limestone did not actually burn, but when heated to a dull redness at about 500° Celsius(C) it began to decompose .Temperatures of around 800 -1000 degrees C were required for a complete burn and the process probably took 5 - 10 days with a cooling period of 3 - 4 days thereafter.

CaCO3 (impure)         ➡       CaO (impure) + CO2
Calcium carbonate - heat ➡ calcium oxide + carbon dioxide (limestone) (burned lime) (gas)

The lumps of ‘burnt lime’ left in the kiln once it had cooled down (variously called lump lime or lime shells), had much the same shape and colour as the original limestone fed in. However, they were porous and much lighter, having lost around half their weight as the carbon dioxide was driven off in the heating process. Emptying the kiln was an unpleasant task, the caustic burnt lime dust was extremely corrosive to the wet skin, nose, throat and eyes and the lump lime had to be separated from the under burnt and over burnt limestone and peat ash by hand. The carriage of the lump lime long distances from the kiln to the fields also had its hazards. If it got wet and began to slake en route, the heat generated in extreme cases could set fire to the cart or creels. But in this un-hydrated form it was easier to transport, being around half the weight and the volume of lime slaked with water.

Applying Lime to the Land

In an age before scientific agricultural advice was available; the application of burnt lime to the land was a procedure involving various local beliefs, customs and practices which had evolved over many years. The amount of time and labour spent on producing lime from limestone meant that it had to be used wisely. Factors to be considered were the type of soil, the intended crops to be planted, the quantities to be applied, the time of year to apply and the stage in the field's crop rotation. Various ministers‘ reports from their parishes in The New Statistical Accounts of the 1840s state that between 16 and 50 bolls of lime per acre were commonly used in cultivation and up to 100 boils on land first brought into use from waste ground. Another complication for the farmer, whether he was inclined to lime his fields or not, was that the Estates laid down strict rules in leases for is application and these could be inflexible and unsuitable for local conditions.

The minister of Kildrummy, whose parish had no limestone, in 1796 criticised the restrictions imposed on the tenants of Glenbuchat Estate:
‘the liberty off allowing their own judgement with regard to the use of lime on their farms, would do more to promote the improvement of the soil than the present arbitrary restriction which evidently discourage rather than encourage their industry.’

Examples of the regulations on the use of lime, stipulated by two estates in the area, come from papers from the 18th and the 19th centuries. Fife Estate, in a tack for nineteen years granted to James McHardy in 1766 for the farm of Torancroy in Glen Nochty, obliged him to use a minimum of 10 bolls of lime annually for each oxgate of his cultivated rigs, under the severe penalty of paying one shilling for every deficient boll.’ (An oxgate was approximately 17 English acres.) By today's values, this rate of application seems very low, but it was probably a realistic quantity reflecting the low output of the clump kilns of the day and the small amount of lime a farmer was able to produce in a season. However, in a letting memo for the 3 - acre Cow Park of Bellabeg for 1832-33, Newe Estate in Strathdon required James Grassick of Coul of Ledmacoy to lay ‘40 boils of lime on every acre with the second crop'. The more efficient draw kilns were in use by this time, hence the requirement for high rates of lime application by the Estate.

We don't have specific details of the methods used for applying lime to the land in the Upper Donside area, but generally used practices in the North East were as follows: the lumps of burnt lime raked out of the kilns were separated from the under or overheated waste, carried to the fields, deposited in small heaps at set intervals and allowed to slake naturally. Alternatively the heaps were covered with soil and slaked over a period of a week or two using the moisture in the soil. Covering the burnt lime heaps gave some protection from the elements, rain and wind, and more control of the slaking process. Slaking the burnt lime could be done more quickly by pouring on water, but this required experience and care.
When water was added, a violent reaction occurred as heat was generated and steam given of and adding too much resulted in a useless lumpy paste.


Ca(OH)2          +          CO2 ➡ CaCO3 + H20
calcium hydroxide carbon dioxide ➡ calcium carbonate water
(slaked lime)



Slaked properly, the lumps of burnt limestone swelled to 2~3 times their original size and crumbled into a fine powder. This hydrated powdered lime was spread on the land by shovel, often while still hot, and harrowed or ploughed in soon afterwards. A mixture of burned lime and peat ash from the kiln made an excellent fertilizer, and dung, turf or other organic matter and soil could be mixed with it to make a compost to eke it out.

Once in the soil, the slaked lime (calcium hydroxide) combined with carbon dioxide in the soil solution to revert back to calcium carbonate, but in a fine form, more readily available to neutralise the acidity of the-soil than the original limestone.

Ca(OH)2          +          CO2 ➡ CaCO3 + H20
calcium hydroxide carbon dioxide ➡ calcium carbonate water
(slaked lime)


Overliming

It was easy to overestimate the beneficial effects of lime. In the mid-18th century, when first generally applied to the land in the North East, lime gave remarkable results in crop yields. But it soon became clear that it was not a universal fertiliser and no long-term substitute for the application of dung, as a farmer from Banffshire reported in 1812:

‘When lime was first introduced in this country (district) as a manure, the stimulating effects were so powerful in producing heavy crops that the fanner thought he could not overdo (it); and hence the system of oats after oats for a succession of 12 to 19 years was so much persisted in, that the soil was reduced to so complete a state of sterility that it produced little else than thistles and other weeds.’

One of the major debates in farming circles, including the farming clubs and agricultural societies, formed at this time to promote improved agricultural practices, was on the best methods of burning limestone .and of application of lime and precious farmyard manure to the land. Used with dung, lime was found to be very effective. Liming the infield cultivation rigs increased the yields of oats and bere over rigs not limed. On the outfield land, more annual crops could be taken before yields dropped and the land became exhausted and left fallow to recover. Liming of the cultivation rigs was considered essential for good crops and those farmers in areas without annual access to lime were at a severe disadvantage. However, the effects of over-liming the land, whereby (as we now know) the pH of the soil was raised above the optimum range of 5.0 - 6.5 for growing most crops, causing problems such as trace element deficiencies, soon became obvious, as the minister of New Deer parish reported in the 1750s:

‘Liming was much used till a few years ago; and can be carried on at a moderate expense. But, although there is plenty of limestone and fuel in the parish, and a kiln for burning it on almost every farm and croft; yet the tenants are now obliged, in a great measure, to discontinue the practice. For it is found that lime, when applied in great quantity, or soon repeated, reduces their soil to a mere caput mortum, producing little but thistle: and other noxious weeds.’

But he emphasises the crucial role it played when breaking in new land and in converting the old cultivation rigs into improved fields:
‘Where barren ground is to be fertilised, or old ridges leveled and improved, the farmer still has resource to it; and when judiciously laid on, it is found to answer his most sanguine expectations.’

On the older-established farms, liming all the land helped break down the distinction between infield and outfield ground, and. when the time came, encouraged the levelling and consolidation of the unenclosed cultivation rigs and the waste spaces between them into the large, flat, stone-walled fields we see today. When used in conjunction with other technical innovations such as field drainage, sown ‘artificial grasses’ and better crop rotations, higher yields of crops resulted. Undoubtedly, without the benefits of lime as part of these improvements, the population of the area would not have been sustained or increased, as it was up to the early to middle 19th' century. Liming the land became associated with modern ‘good farming practice.’ The minister for Abernathy, Elginshire, in 1845, gave his enthusiastic views on the benefits of lime on the improved agriculture of his parish:

‘For a considerable length of time past the improvement in agriculture in this parish has been great; and is likely to continue. This has been occasioned chiefly by the command of lime, which happily is found here in various places: and the abundance of peat and decaying timber, for burning that valuable article is found all over the parish. This mode of cultivating and improving the ground is found so beneficial that there is not an individual amongst even the lower order of farmers (such as pay no more than £5 of rent annually) who has not o limekiln in use. This manure not only promotes the increase of corn, &c., but greatly meliorates the pasture for cattle, and increases both quantity and quality of hay.’

When were the Limekilns built?

Because of their appearance of great antiquity, putting an accurate date to their building is not straight forward, as none of the records examined so far give precise dates. The minister for Strathdon, in a knowledgeable and detailed account of the agriculture of his parish in the early 1790s, reported that there was an abundance of local limestone but little use was made of it. His successor writing in 1839 in an equally detailed account, states that nearly every farm in the area had a limekiln. These reports indicate that the stone-built farm kilns, marked on the first edition OS maps of the late 1800s, the remains of which we see today. were built between the early 1790s and the late 1830s.

In Glenbuchat, the minister’s accounts of the agricultural scene are less informative. The more detailed estate papers give a picture of small-scale, local, lime producing activity from the mid-18th century onwards, but with strict restrictions on supplying it out with the Estate (see appendix I). However, they do not distinguish between the use of clump kilns or draw kilns: commercial clump kilns were still being used in the North East in the 1840s.

A study of the distribution of the kilns on the 1st edition OS maps of 1869 - 70 suggests that they were associated with the individual farms of the post improvement landscapes, i.e. they were built after the reorganisation of the lands by the various Estates from runrig cultivation into separate, single tenanted holdings. For the remote Upper Donside area this was in the late 18th and early 19th century (although variation in progress by the different estates would have taken place, depending on the enthusiasm for improvements of their Lairds).

In an attempt to narrow down the time period when the general adoption of farm limekilns in the area took place, we can speculate that one impetus for building them came with the boom in agriculture resulting from the French and Napoleonic Wars (1793 - 1815).Tenants responded to the stimulus of higher cattle and grain prices by upping production and where possible, increasing the area of their arable land. Waste ground was taken into cultivation fields were enlarged and enclosed and an increase in farm sizes and the number of new holdings resulted. Greater demand for lime, as agricultural improvements took off, required more efficient production of it, by the use of draw kilns, and many of the tenants of these newly laid out farms and crofts built limekilns on their holdings at this time.

Lairds sought to benefit from the relative increase in prosperity by maximising their rental incomes, and rents rose dramatically as competition for farms increased during these years. When the war ended, however, the resulting slump in prices hit the tenantry hard. The Duff House Papers give an indication of the severity of the post-war depression felt locally by a number of petitions to Lord Fife for rent relief.

For example, from John Forbes tenant of Beltimore, one of the larger farms in the Glen: 12th December 1820
‘That your petitioner has been Ground Officer to your Lship and Family of Fife upwards of thirty years - That your petitioner having renewed his lease during the late war, was induced to offer a very high rent, indeed triple the former. That the peace and consequent depreciation of all kinds of farm produce, together with the bod crops of 1816 and 1817 rendered it impossible for your petitioner to pay the stipulated rents - whereby your Lships petitioner has fallen into arrears and finds it impossible to discharge the same.’

Another factor which probably encouraged kiln building was the laying down of the turnpike road through the Upper Donside area in the early 1820's and the resulting improvement in local and estate roads. The transport of limestone and peat by horse and cart, in larger quantities and for greater distances, to kilns built on farms further from the quarries and peat mosses was now more practical.

(There is a report of lime from limekilns in Corgarff being carted to Deeside for the reconstruction of the royal castle:

‘After Prince Albert, Queen Victories Consort, bought the lands of Balmoral in 1852 they lived in the old castle, but plans were put in hand for the erection of a larger house able to accommodate a Queens’s retinue and guests. When it was built between 1853 and 1855, my grandfather (James McHardy of Bumside of Corryhoul) carted lime for the Building.)

In lower Strathdon, the end of the Fife Laird's ban on access to limestone from the Balloch quarries in Glenbuchat, sometime after the 1820s may also have resulted in more kilns being built on the farms of that district (see appendix l).

The minister of Strathdon was able to report in 1839: ‘Within the last twenty years, very great and rapid progress has been made in agricultural improvement by trenching, drainage etc. many of the tenants have made considerable additions to the arable land of their farms. The facility in the command of lime is of material benefit in this respect.’

A gradual rise in the profitability of farming, from the 1840’s up to the late 1870s_when more food was required to feed Britain's expanding industrial cities, and before foreign competition from imports affected farm commodity prices, probably promoted further building of limekilns on farms of the area. Some kiln building apparently continued beyond the late 1860s. An additional 6 farm limekilns are marked on the second edition OS maps of 1902 - 03 which were not present on the 1869 - 70 first edition maps.*
(*The OS maps have proved to be accurate in the information they display, but an occasional apparent inconsistency appears on them. The limekilns at Badenyon (NJ 3422 1894) and Easterbuchat (NJ 3892 1542} in Glenbuchat are not marked on the 1869 OS map, but they are present on the slightly earlier Estate map of 1864. Also, the prominent kiln at Stroin (NJ 3512 1007) in Glen Carvie is neither marked on the first edition (1869) nor the second edition (1902) OS maps.)

It is noticeable from the OS maps that on the larger, more commercial farms of the area limekilns were absent. For example, the Mains of Glenbuchat, The principal farm in the Glen extending to 181 arable acres in 1864 and the farmlands of Buchaam, Invernettie and around Candacraig House in lower Strathdon had no kilns. However, they would have been the largest users of lime for their extensive fields. It is probable that they found it more economical to buy burnt lime from their smaller neighbours than to make it for themselves in the years before commercial supplies became available with improved roads and rail links, in the latter half of the 19th century.


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Picture added on 06 August 2015 at 20:35
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Kilns

23 Lime Kiln at Ryntaing Glenbuchat c 19809 Part 8 Kilns: Appendices9 Part 8 Kilns: The Survey8. Part 7 Kilns: The Decline of Lime Burning6 Pasrt 5 Kilns: Estate Reorganisation4 Kilns Part 4  New Holdings4 Kilns: The Peat Mosses 3 Kilns Part 22 Kilns: Introduction1 Limekilns of Upper Donside