0
2000000
4000000
6000000
8000000
10000000
12000000
1700
1720
1740
1760
1780
1800
1820
1840
Year
Ti
n c
oi
ne
d
(
lbs
)
Cornish tin
production
Devon tin
production
18th Century and lasting until the 1830s (Greeves 1996). Cornish output reached a peak around 1780, declined slightly around the turn of the century, but afterwards rose to hitherto unmatched levels.
Table 1.5: Tin Coined in Devon and Cornwall in the 18th and 19th Centuries (Data from Lewis 1908 p256-8)
Year Tin Coined in Cornwall Tin Coined in Devon 1700 3151504 lb (1432502 kg) 47384 lb (21538 kg) 1720 3302440 lb (1501109 kg) 5464 lb (2484 kg) 1740 3795578 lb (1725263 kg) 0 lb (0 kg) 1760 2717 tons (2464862 kg) 1780 2926 tons (2654467 kg) 1800 2522 tons (2287958 kg) 1820 2290 tons (2077488 kg) 1837 4790 tons (4345488 kg)
The coinage system was abolished in 1838. Later production figures were compiled by the Mining Record Office, and published in annual volumes as ‘Mineral Statistics of the United Kingdom of Great Britain and Ireland’.
Ore output from 1852 to 1913 for Devon and Cornwall has been summarized by Burt et al (1984 Table 1, 1987 Table 5), and shows that Devon continued to produce a small quantity of tin (amounting to approximately 1% of the total UK output) for much of the remainder of the 19th Century, and into the 20th, with 97 tons (87,998 kg) of tin ore being recorded as late as 1913 (Burt et al 1984 Table 1). By contrast, Cornish ore extraction increases steadily up to 1871, peaking at 16,759 tons (15,203,765 kg) – equating to a metallic tin output of 10,900 tons (9,888,480 kg) (Hedges 1969 p13) – falling off very slightly thereafter but remaining relatively stable at around 13,000- 14,000 tons (11,800,000-12,700,00 kg) for the rest of the 19th Century, then after
suffering another fall in 1896, stabilizes once again at around 6,000-7,000 tons (5,440,000-6,350,000 kg) (Burt et al 1987 Table 5).
With increasing industrialization, the costs and capital outlay involved in setting up and maintaining smelting furnaces escalated; from the 18th Century there is a shift to
ownership by partnerships and companies owned by shareholders. Business records and accounts provide much information regarding smelting houses and the workings of the tin trade at this time. An overview of the subject has been provided by Barton (1967, 1968, 1971).
1.4.7.2: Ore Extraction
Documentary evidence makes it clear that lode ores were providing an increasing majority of the ore for tin smelting. In Cornwall, in coastal areas, particularly in the Penwith and St Agnes mining districts, there was exploitation of cliffside outcrops. Pryce (1778 p20) refers to mines ‘at or near the sea cliffs’.
Many more shaft mines were opened, and with advances in pumping technology to remove water from the lower levels – notably the introduction of the steam engine in the second decade of the 18th Century, and plunger pattern pumps in 1810 – these were delved to ever-greater depths. Collins (1912) and Dines (1956) provide extensive lists of hundreds of Cornish mines, not all of which were purely for tin.
After c.1700 deep mining using shafts and adits appears to have been preferred over opencast methods in Devon (Greeves 1981b; Gerrard 1997 p104). This was on a far smaller scale than in Cornwall, but around 50 tin mines are known to have operated in the 18th and 19th Centuries (Dines 1956; Harris 1968 p26, p45).
Despite the growth in shaft mining, alluvial deposits continued to be exploited through into the 20th Century. Streamworking clearly remained of sufficient importance to merit inclusion in the works of Pryce (1778 p131-5), Borlase (1758 p161) and Hitchens and Drew (1824). Even in 1855 Leifchild (p202) records that ‘Although the richest deposits have been well worked, and the ground turned over probably twice or thrice, the tin stones rejected at one time becoming valuable at another from their comparative scarcity, yet there remains still enough to prevent tin streaming from becoming extinct in Cornwall’ and twenty years later Collins also describes the practice (1875 p33). Higgans (1979) draws attention to the Angarrack Smelting House (SW583382) coinage books, which survive up to 1741 and record the receipt of stream tin (Bolitho Records DDRG 1/122-7 CRO). Henwood (1873/4) reported that in 1873 the total output of stream tin from Cornwall was 50 tons (45360kg).
A Bodmin Moor resident has reported that streaming was carried out by farmers, working part-time during the quieter times in the agricultural year, up until the late 19th Century (Gerrard 1987), and streamers working at Red Moor (c.SX0661) were
photographed some time at the beginning of the 20th Century (Embrey and Symes 1987
p16).
Streaming in Devon appears to have been limited in this period, but recorded examples include ‘Rendals Streamworks’ at Rundlestone (SX579750) in the 1790s (Greeves 1994), and ‘Wheal Providence’ in the parish of Sheepstor (c.SX5667) in 1815 (Cook et al 1974).
Further support for the use of both types of ore, at least within the 18th and early 19th Centuries, comes from contemporary accounts of smelting which make it clear that
mined ore and alluvial cassiterite were often smelted using different techniques (see p154).
The old rules that prohibited the removal of black tin from the Stannary in which it was raised were no longer in force by the 18th Century. Although it is likely that the small amounts of black tin raised by streamers would still be sold to local smelters (Barton 1968 p140), ores were sometimes transported long distances. Examples are provided by Henderson (1912), who gives a list of parishes and individual mines that provided ore for the Newham Smelting Works (SW829441) in 1707, and Barton (1968 p140) quotes similarly long lists of mines that supplied Calenick Smelting House (SW820440) near Truro in 1829 (Account Book of Tin Bought, Calenick, 1828-36, DDRG 1/150/61 CRO) and Trereife Smelting House (SW455294) near Penzance in 1890 (Trereife Black Tin Purchases Book 1883-91 DDRG 1/114 CRO). Greeves (1996) notes the following examples of ores being taken from Devon into Cornwall: records exist showing ore going from Vitifer Mine (c.SX6881) to Calenick Smelting House in 1791 and 1798 (CRO/DDRG 1/128-141, June 23 1791; CRO/DDRG 1/128-141, 6 April 1798), from Vitifer to Penzance in c.1797 (DRO 564/Vol 16, p1), and from
Whiteworks Mine (SX612710) to Calenick in 1790 (CRO/DDRG 1/128-141, 7 July 1790).
Although restrictions on the movement of tin ores between districts had been lifted, the export of British tin ores was still prohibited (Leifchild 1855 p203). However, some ores were beginning to be imported from abroad; Leifchild (1855 p213) refers to Malaysian ores.
From 1859 onwards, Bolivian ores were bought for smelting at Charlestown
72% metallic tin (compared to 62-65% for Cornish ores) (Thibault 1908 p190), but contained impurities that made them troublesome to smelt, with the result that other companies that purchased South American ores initially lost money (Barton 1967 p129; 1968 p142). Later, only the better quality ores were smelted in Cornwall, poorer grades being sent to Germany (Thibault 1908 p190). Ores from Australia were also smelted at Charlestown (Charlestown Shipwreck & Heritage Centre 2006).
1.4.7.3: Ore Processing
Ore processing continued to be a requirement. Leifchild (p204) reports that in 1855, larger pieces were broken up using hammers and then the ore was crushed using stamps. The wooden stamping machinery illustrated by Borlase in 1758 (Plate XIX), and the descriptions of stamps and stamping given by Pryce in 1778 (p328) and the writer who visited a mill near St Ives in 1780 (Swete 1971), do not appear markedly different from the stamps of the previous century. However, refinements in the design of stamping and dressing machinery did occur: mortar stones went out of use in the 1700s, being replaced by composite rubble heads (Gerrard 1997 p92); around 1805, waterwheels were replaced by steam engines (Earl 1991); and, by the second half of the 19th Century, Californian stamps were being introduced, which were much more effective as they had a stamp head that rotated as it hit the ore (Gerrard 1997 p92). There was also a move towards having separate stamps and smelting houses (Brooke 1998 p49), so that dressing of the ore often took place at the mine and the resulting concentrate would subsequently be sold to an independent smelter (Leifchild 1855 p203; Earl 1991).
The dressing of the crushed ores also benefited from a range of new developments, including the circular buddle, tossing tubs, trunking boxes and shaking tables (Gerrard
1997 p92). The details of these are beyond the scope of this work (Leifchild 1855 p204- 7 gives a summary); suffice to say that the dressing process became more efficient. In 1792 batches of black tin assayed at Calenick were said to contain between 45 to 63.7% tin. Complaints were lodged regarding the poor quality of those lower yielding batches (Tylecote 1980a).
In the opening years of the 20th Century, Cornish ores were being dressed to produce concentrates containing between 79 and 82% tin oxide (62 to 65% metallic tin), the main impurities being silica, iron oxides and some tungsten (Thibault 1908 p190). One of the difficulties arising from the ever-increasing demand for cassiterite was a decline in ore quality. Ores that were not ‘clean’, i.e. were composed of cassiterite mixed with various other chemical species, had previously been rejected on the grounds that it was either not possible to remove these impurities, or that it was not
economically viable to do so.
It is true that good quality ores were still obtainable in the 18th and 19th Centuries (e.g. ores from Eylesbarrow Mine (SX5968) (Cook et al 1974) and the vein ores of the St Austell area (Barton 1967 p25; Hamilton-Jenkin 1967 p9 quoting Philip Rashleigh MSS, Catalogue 1797 RIC)), and Leifchild (1855 p204) reports that ‘From rich veins a large proportion of the ore is obtained in a pure state, and then it is only necessary to break down the large irregular masses into fragments of a tolerably equal size to render it fit for the furnace’. However, by the 18th Century, it was considered necessary to attempt to clean and utilize poorer grade ores – black tin that was, according to Leifchild (1855 p208), ‘associated with iron, copper, and arsenical pyrites, and with wolfram’, and new methods were developed to accomplish that.
Sulphide minerals containing species such as arsenic, cadmium and lead could be roasted in an oxidizing atmosphere – a process known as calcining – and the majority of the contaminants would be driven off as vapour (Thibault 1908 p146; Wright 1982 p64; Smith 1996). The practice of calcining tin ore in tin kilns was established in the 17th Century, and was first described by The Inquisitive Person in 1670 (Anon 1670) (see p116). During his visit to Cornwall in 1725, Kalmeter noted that ‘In St Agnes mining district they recently started to burn or roast the ore …in a lime kiln,
particularly if it is hard, as afterwards it is much easier to stamp. … In the places and at those mines where the ore is mixed with mundic or sulphur pyrites it must first be roasted and these impurities must be completely burnt out, for which they have their burning houses or calcining houses, and furnaces’. He then went on to describe a burning house and the process of calcining (Brooke 1998 p50, p341).Hitchens & Drew (1824 p618) report that ‘About four fifths of the ore raised from mines is infected with mundic; in consequence of which it must be purified in the burning house...’
A very well preserved example of such a building is the ‘blowing house’ at Godolphin (SW60333205), which has the date 1784 inscribed on a stone on one wall, and is described as a ‘burning house’ on the estate maps of 1786 (CRO RH 210). Schofield (1968) provides a detailed description of this building, while misinterpreting its purpose.
Impurities other than arsenic and sulphides were not so easily handled. Calcining was not effective in eradicating tungsten and bismuth, nor would it remove iron minerals. By the mid 19th Century chemical methods of separating impurities from ore had also been developed. Leifchild (1855 p208) notes that a ‘new process’ could thoroughly clean ores containing tungsten minerals (Thibault 1908 p154), though this was only
available to the larger operators for economic reasons. Tungsten, which previously had reduced the value of the tin ore, thus became a saleable commodity in itself.
From about the 1840s ores containing iron oxides were cleaned by leaching with acid (Barton 1967 p91), as were calcined copper bearing ores (Thibault 1908 p156-7). While these methods of treating tin ores were highly successful, the variation in quality of tin concentrates led to their being smelted in slightly different ways.