The Cornish Vanning Shovel Bryan Earl

The Cornish Vanning Shovel Bryan Earl First published in Tools & Trades Volume 10, 1997 A Shovel big enough to be a collier's banjo,I but made of light, 16-gauge, mild steel: here is something special, the Cornish Vanning Shovel. Its Function was to "try" or assay ores. On Vanning, and Assaying Generally Of entrancing simplicity, when properly used the shovel becomes a refined and pre cise instrument. In skilled hands it can reveal not only the presence of a whole range of valuable ores, but also their con centration. Its greatest use was by miners in the West of England for examining tin ores: rocks holding the mineral cassiterite (Sn02). Such ores are considered rich if they hold 5% are more of metal, valuable down to I % and workable, by the legendary "tinstreamers", down to 0.1%. The tin streamers were "tinners" who chiefly made their living by extracting the values left in stream and river beds, originating either from the natural breakdown of lodes, or discharged as waste "tailings" from a mine. Tinners also frequently bought orestuff from workers who had small mines or who picked over old mine dumps but did not have the resources to treat the "stuff' to reach a grade of tin con Wilfred Bray making a vanning assay in the South centrate that could be sold to a "blower" or Crofty assay laboratory. Apart from assaying he was a . talented musician and composed for his harmonium, are smelter. The are matenal Itself, the including a rousing "South Crofty" - unfortunately the cassiterite, is usually of a drab brown score for this appears to have been lost The la~e Frank colour entrapped in waste "gangue" rock Hutchm, chief assayer of the mme, considered him to be .' . the finest vanner in Cornwall. (1967) mmerals, WhICh also often have a brown colour - mostly from the iron oxides which are frequently associated with tin ores. But let a miner or "streamer" crush up some orestuff, take a handful of the powder, put it on the vanning shovel with some water, and in a matter of minutes he can make an evaluation down to less than 0.1 %. This was the ancient "trial" for tin. The rule a skilled streamer 36 worked to was: "If I can see it, I'll buy it". That is, if he could throw up even a small "head" of the, usually light brown, cassiterite, from a handful of ore after due manipula tion, it would be worth his while making an offer to buy the orestuff, or work it at a nego tiated price. His livelihood depended on this judgement. A variety of other orestuffs could also be assayed with the shovel. For example the grey copper ore, redruthite or chalcocite, CuzS, or contaminating minerals such as arsenopyrite, AsFeS. The vanning technique was certainly well known by the 16th century (Bearez 1565) and was still in use to control the valuation and working of a major Cornish tin mine (Geevor) until 1985. However, it only showed the amounts that could be expected to be won by traditional washing methods. In the 19th century more modern techniques such as the wet Pearce titration assay, or more recently X-ray fluorescent methods, were used to determine the total metal content of a sample and so indicate the amount of tin left unrecovered and usually lost in the waste tailings. These new techniques now allow comparison of the amount of tin won with the total amount originally in the ore and thus provide a check on the highly efficient flotation process that came into use in the 1980s. The vanning assay depended on the ability to throw the heavy constituents of a well crushed ore sample further through water than the lighter, usually waste, portions. The work was usually done over a "kieve" - a large tub filled with water. For best results the blade was prepared before use by rubbing with sharp sand or pumice to give it a slightly matt surface. The sample, mixed with water, was first swirled round and round on the shovel to settle the denser fractions under the lighter ones. The shovel was then given a series of upward flicking motions, "vanned", so that the underlying heavy values were thrown upwards and forwards away from the lighter parts. This formed a distribution of minerals on the shovel blade "like a bullock's tongue", the heavy material showing as a crescent patch ahead of the less dense fraction. A skilled vanner could there and then make an esti mate of the value of the ore. It a handful yielded a head the size of an old shilling, a "shilling van", the ore held about 1% of recoverable tin. There were many refine ments the vanner might use during his examination. Manipulating the shovel so that the water flowed back over the sample could assist separation. Tapping the blade at certain points would help in the separa tion of minerals of nearly equal density. A really skilled vanner, such as the late Wilfred Bray of South Crofty Mine with an almost magical touch, could separate at least two heavy constituents on the shovel as two individual heads and evaluate their The copper pattern for the vanning shovel 37 Heating the 16 gauge blank with the "lamp". The blank becomes concave towards the flame Lowering the female die into place 38 concentrations. This he did in a matter of minutes, outstripping modem techniques. In addition he could tell to what degree the ore should be crushed to get the most effective separation of the values from the waste. Undercrushing leaves good material buried in waste rock; overcrush ing allows part of the stuff, both values and waste, to be reduced to "slimes" which are carried away in wash water. At its simplest the trial could be made on the spot, crushing the material with a hammer on the shovel before vanning it. A fully developed trial was carried out as follows: a sample was put on an iron plate, about three feet square and half an inch thick, let into the floor of the sample room. The orestuff was pounded by repeatedly dropping an iron beating head with a wooden shaft onto it. The coarse powder thus produced was reduced in bulk by coning and quartering. A portion Sledging the dies to press the blank into shape. Donald of this was ground "as fine as pepper" on Semmens, on left, fonns the haft socket an iron or cast steel "bucking plate" using a flat-faced bucking hammer. Here the material was first beaten finer and then the hammer was used to grind it, the operator pressing the hammer head down with one hand and rubbing it round in circles with the other. The amount needed for a careful assay was then measured or weighed out. Prior to the l860s this amount was a half-noggin wine measure, filled and levelled across the top. After an initial vanning, the material was dried and roasted to dull red heat in a crucible, while being stirred, to bum off sulphides and arsenides which could falsify the result. The charge was then re-vanned and a hare's foot was used to separate and brush off the "head" from the waste "tails". The cassiterite con centrate head - known as "black tin" although it was normally light brown in colour - was weighed in pennyweights, incorporating a factor to allow for the losses expected with the old fashioned methods. Another system used Troy weight for the sample and Avoirdupois for the head after it had been dried by holding the shovel over the sample room fire which also had the important functions of keeping pasties hot and brewing tea. An even more mixed-up system was used in the rule of thumb "every pennyweight of tin produced from a sample of one gill, win measure, gives 160 pounds black tin in one hundred sacks of 18 gallons each, beer measure". This meant that instead of 160 pounds, the actual weight of black tin was 240.932 pounds. Avoirdupois, the difference of 80.932 being sup posed to make up for smelting losses. "Sacks" varied in size from district to district, and could be 8,9,12 or 18 gallons beer measure. The smelters, of course, used all this to their advantage when buying the black tin. By the late l860s the system of reporting value had changed to the one used until the 1980s. The head was then reported as so many pounds of black tin per ton of orestuff, the 39 same weight system being used for both sample and concentrate. One mine however, Do1coath, then the most important mine in the West of England, had adopted a system of its own early in the 19th century. This was similar to the "assay ton" technique used for assaying gold and it gave much closer results. The final change was to express the value as the percentage of metal held by the orestuff. Removing the formed shovel from the dies The black tin concentrate itself was assayed. A different method of assaying had to be used as it was found the vanning technique gave varying results when applied to high grade concentrates. The sample of concentrate, weighed in special "20-weights" (about 2 ounces), was fired in a crucible with culm (anthracite powder) or cyanide to reduce the cassiterite to metal. The tin produced was also weighed in 20-weights and the result was reported as so much "in twenty". This was the "fire assay". On the Vanning Shovel Itself The manufacture of the shovel was specialised work.

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