From ore to cauldron

Sentences without a label are documented facts; the others are marked "probable" or "uncertain".

The copper of the Orco and Soana valleys comes from an ore rich in sulphur, chalcopyrite, which has to be roasted and smelted several times before it becomes metal. Then the copper is beaten at the tilt hammer, finished by hand, cleaned with acids and coated with tin. This page follows the metal from the mine to the kitchen and tells of the work of the magnins, who travelled about repairing and tinning pots and pans, with the chemistry behind each step.

The ore: chalcopyrite

The ore of the Canavese mines is chalcopyrite, which contains about 35 per cent copper and a lot of sulphur. Bussi shows it from the mines of the Val Soana and the Vasario side valley, and OpenStreetMap indicates it at the first of the five entrances of the “Miniera di Caramia”, above Sparone. The oldest mining centre lies above the hamlets of Vasario, in Sparone, and Ceresa, in Ribordone, with open-cast workings and tunnels; the Ceresa 4 mine, at 1432 metres, goes about 300 metres into the mountain. At the Coccagna, above Noasca, and at the “Reale” of Valprato the chalcopyrite occurred together with galena, from which silver was obtained.

The yields given by eighteenth-century travellers differ. In 1785 Galleani Napione writes that the copper pyrite of Sparone gave about 20 per cent of “très-ductile” copper; in 1786 Nicolis de Robilant gives a yield of 8 to 10 pounds (libbre) of copper per quintal. The ore was sorted and broken on the small yards in front of the mines and then carried to the copper works (ramere) in the valley floor by small caravans of muleteers, or on people's backs where an animal could not pass.

Chalcopyrite is a copper iron sulphide, CuFeS₂. With the atomic masses of copper (63.5), iron (55.8) and sulphur (32.1), copper accounts for about 34.6 per cent of the formula by weight: this is Cima's 35 per cent. The ore as mined, however, is not pure chalcopyrite, because it is mixed with the rock, the gangue: that is why the real yields are lower.

Sources: Cima 2025a, pp. 9, 22, 49-52, 55-59, 64-65; Bussi 2026, p. 24; OpenStreetMap

Roasting and smelting

Cima divides the work into four phases: extraction and sorting of the ore; reduction to metal as far as rosette copper; hot beating at the tilt hammer, the “cavatura”; cold finishing with hammering, trimming of the edges, handles and tinning of the inside. For the second phase the chalcopyrite has to be roasted several times. Then it is loaded into the shaft furnace, in layers of charcoal and roasted ore, and first the “metallina” (matte) is obtained, then the “rame nero” (black copper); the final refining takes place at the cupel, in a forge fire. According to Cima, in the sixteenth century smelting was done in small heap furnaces, and the shaft furnaces, smaller than those for iron, arrived in the seventeenth century, still with three remeltings.

At Castellaro there remains the only shaft furnace for copper preserved in Piedmont: a quadrangular tower with a chamber of about 50 by 40 centimetres and the circular crucible at its base, lined inside with refractory bricks, 3-3.5 metres high and charged from the top. The cupel is a hollow of refractory earth of 40-50 centimetres: for 20-30 kilos of metal it took several hours of continuous blowing and light charcoals, such as chestnut, birch or fir, because charcoals that are too strong “burn” the copper. The smelters worked in front of the furnace at over 1000 degrees.

The master checked the copper by dipping into the bath the “saggiolo”, an iron rod coated with refractory earth, and testing the film of metal that stayed stuck to it. Sala, who observes the Giovando forge at Sparone in the Thirties, describes the same test: the thin sheet of copper was bent and hammered and, if it did not break, the copper could be poured. There the crucible was made on the spot with refractory earth from Castellamonte.

In roasting the sulphur burns and becomes sulphur dioxide, while part of the iron is oxidised. In the furnace the remaining copper and iron sulphides melt together into the matte and the iron oxide passes into the slag; further oxidising steps remove the rest of the iron and sulphur and leave black copper, still impure. At the cupel the air oxidises the last impurities, which go into the slag. Pure copper melts at about 1085 degrees.

Sources: Cima 2025a, pp. 21-26, 40, 67-68, 73, 75, 92; Cima 2025b, pp. 149-151, 154; Bussi 2026, p. 27; Cima 1987, p. 46

The rosette, the copper that travels

Rosette copper is semi-finished copper in cakes, of 99.6 fineness. In the mid-eighteenth century the “Descrizione” of the province of Ivrea says that the copper forges worked ore from the Valpelline, in the Duchy of Aosta, “there reduced to rosette”. In 1716 the Signorelli forges at Cuorgnè had bought 490 rubbi of rosette copper from the Bauni of Milan and partners, for 10,332 lire. In the nineteenth century the Canavese copper works were still working at full capacity, but the ore came from elsewhere; Cima thinks that metal arriving through wider circuits, at a lower price, caused the crisis of the local mines probable.

At the Giovando forge, in the 1981 photographs, the copper remelted in the cupel hearth is poured into the refractory-earth moulds of the casting bench: out come “plano-convex cakes” which, turned over, go straight to the tilt hammer. The rosettes, still hot, were beaten a first time to make use of the heat of the casting and became concave discs.

Sources: Cima 1981, p. 122; Cima 2025b, pp. 154-155, 211, 228; Cima 2025a, pp. 26-27, 48, 72, 120; Cima 1987, p. 46

Beating: the cavato

Beyond a certain size the discs were beaten in a stack of six to eight pieces enclosed between two “camicia” (jacket) forms; each piece was wetted in water with refractory earth so that it would not weld to the others. With the cavatura at the tilt hammer, alternated with reheatings and with swapping the pieces within the stack, walls on average under a millimetre were reached; then the edges were trimmed and the two jackets went back to be melted. The forger had to give the vessel a thicker bottom and thinner walls. In the copper forges the head of the tilt hammer was an elongated truncated cone, suited to concave shapes; in the iron forges it was flat.

The forger moved the glowing stack with tongs and a hook and adjusted it with his foot, protected by a thick jute legging that was always wet. Among his tools were “pelican-beak” tongs for concave shapes and a two-pronged fork for taking hold of the hot rosette. In the 1947 photographs the old master Aimonetto of Sparone turns the stack of forms with two pairs of tongs in time with the blows, so that the tilt hammer does not strike twice in the same spot.

Copper is very malleable, but when beaten cold it hardens and becomes brittle, because the crystals of the metal are deformed: this is work hardening. Heating it, annealing, makes it workable again. That is why the cavatura alternates blows with reheatings. The refractory earth between the discs acts as a separating layer: it prevents two clean copper surfaces from welding together when hot, under the blows.

Sources: Cima 2025a, pp. 6, 69-70, 72, 74-75, 80; Cima 2025b, pp. 144, 240; Bussi 2026, p. 27

Finishing: acid, hammer, handles

The cauldron makers (paiolai) finished the vessels raised at the tilt hammer on the “cavallo” (horse) and on the “palo” (post), usually in a department of the forge; there were also workshops that bought the rough cavati and finished them. The cauldron maker washed the rough copper with nitric acid and water, beat it on the “cavallo” for the sides and on the “palo” for the bottom, finished it with a wooden mallet, fitted the handles with an iron ring or with rivets and tinned the inside. The workshop also had a small forge with bellows, a steelyard, a tank for nitric acid, foot-operated shears and boxwood mallets, as well as chisels and gravers for the decorations.

Dipped in dilute nitric acid, the brown, blotchy forms turn bright orange. Repoussé decorations were made on the vessel filled with pitch or wax. A nineteenth-century cauldron from Sparone, raised at the tilt hammer and tinned inside, has its handle and rim ring in iron and its lugs in brass. Production was mainly of kitchenware, cauldrons, large boilers for the dairy products of the summer pastures, baking pans, plates and stills. Polenta cauldrons were among the few cooking vessels without tin: they were scrubbed with sand at every use to remove the oxides.

In the heat of the forge copper becomes covered with a dark layer of oxides. Dilute nitric acid dissolves them and leaves the metal exposed, with its own colour. Sand does the same job by abrasion.

Sources: Bussi 2026, p. 27; Cima 2025b, p. 241; Cima 2025a, pp. 45, 67, 76, 81-83, 88

Tinning

Tinning the inside made it possible to use copper ware without poisonous oxides forming. Paviolo describes the stages. First the “grematura”, the vessel passed upside down over the forge; then cleaning with muriatic acid and a clod of turf, the “teppà”, and with hemp tow; washing; a pass with “acido cotto” (cooked acid), muriatic acid with sal ammoniac and zinc. The molten tin was poured into the heated vessel and quickly spread with tow or a piece of leather. At least three passes were needed, for an average polentino 50-60 grams; at the end it was polished with ash and vinegar. In the jargon (trade slang) of the magnins tin is “corent”.

The tin was an alloy with lead, usually 20 per cent, and for soldering half tin and half lead was used. Hygiene regulations did not allow lead, and a manual of 1924 recommended 10 per cent; anyone who raised the share of lead to save money called it “giacu” in the jargon, so that the customer would not understand. In the small forge at Buttifinera, under the stove, there were cakes of tin, one of about 850 grams.

Muriatic acid is hydrochloric acid. With zinc it forms zinc chloride, which together with sal ammoniac, ammonium chloride, acts as a flux: it dissolves the last oxides and protects the hot metal while the tin, which melts at 232 degrees, wets the copper and adheres to it. The compounds that copper forms with acidic foods are toxic, as is lead: that is why the tin layer had to be continuous and low in lead.

Sources: Bussi 2026, pp. 27, 29; Paviolo, pp. 63-65; Cima 2025a, pp. 78, 129, 132-133; Nigra 1874, p. 58

The work of the magnins

In the copper production chain Bussi distinguishes smelters, hammerman, cauldron maker and magnin: the magnins went round villages and hamlets to sell the finished product and sometimes to collect scrap for remelting. Often the magnin was also a craftsman who stopped in the squares to repair worn objects on the spot. He was self-employed, but depended on the entrepreneurs at the top of the production cycle; the copper works supplied him with copper and roughed-out cauldrons, even on credit. In the jargon of the trade the magnins call themselves “ruga”. The coppersmith went over and replaced the iron rings, changed the rivets of the handles and patched holed pans with pieces of copper called “biane”; the tinsmith carried a small bellows or a fan and heavier equipment on a wheelbarrow.

The trade is old. As early as the visitation of 1545 Marruchi writes that every year more than half the people of the parishes left for other provinces, some begging, some “reparantes supelectillia stanii”, that is, repairing ware with tin. The magnin carried a small post anvil, a portable bellows, a bottle of dilute acid, hammers, a file, tongs and a copper soldering iron to be heated red-hot on the embers. The makeshift forge on the ground burned dry wood or charcoal, usually given by the farmers. The boy, the famàut, looked for work by shouting “Si stagnan le pignate e le padele” (we tin pots and pans). The magnin sold the vessels by weight, sometimes counting the iron as copper too.

In 1822 a survey counts in copper 34 people in the foundries, 43 in the cauldron makers' workshops and 6 in those of the magnani, but Cima warns that the 6 are only those with a fixed workshop: the numerous itinerant workers of the Orco valley are missing. The magnins worked copper, tin, lead and acids without gloves or masks and many died young; Paviolo says, however, that it is not known how many died because of the trade and how many because of their disorderly life, poor food or pneumonia uncertain.

Sources: Bussi 2026, pp. 27, 29; Cima 2025a, pp. 78, 83-87, 142, 153; Cima 2025b, pp. 96, 232-234; Paviolo, pp. 56, 60, 62-66

Remelting copper

Copper was not thrown away. The Signorelli forges took back broken copper for remelting, paying “two lire for each rubbo”; for Cima they worked almost only semi-finished copper in cakes and smelted only to recycle scrap. After the middle of the nineteenth century three forges were still working at Sparone, one with a foundry, which remelted scrap, perhaps because the Vasario and Ceresa mines had closed. Some magnins were simple travelling sellers who took the vessels on sale-or-return and collected scrap to be remelted at the copper works. For Cima the itinerant coppersmiths of the Orco valley got their supplies of “new copper”, semi-finished, from the forges of Pont and Cuorgnè.

Copper can be melted again without losing its properties; melting scrap costs much less energy than extracting the metal from the ore, because there is no need to remove the sulphur or the iron.

Sources: Cima 2025a, pp. 46, 83, 118; Cima 1981, pp. 119-121

For the class

A calculation to try. Chalcopyrite contains about 35 per cent copper and Robilant, in 1786, gives for Sparone a yield of 8 to 10 pounds of copper per quintal of ore, that is from 8 to 10 per cent. How much chalcopyrite was there in the ore as mined? Solution: from 8/35 to 10/35, that is between about 23 and 29 per cent; the rest was gangue.

Second question. To tin an average polentino 50-60 grams of tin are needed, with 20 per cent lead. How much lead ends up in the polentino? And with the 10 per cent of the 1924 manual? Solution: from 10 to 12 grams in the first case, from 5 to 6 in the second. Third question: in 1748 the Magnino workshop at Chivasso had about 35 rubbi of copper, with the rubbo at 9.221 kilos. How many cauldrons of about 3 kilos could be made from it? Solution: about 323 kilos, that is about a hundred cauldrons, as Collini calculates, without counting the waste from the edges.

Sources: Cima 2025a, pp. 9, 22, 49-50, 164-165; Paviolo, pp. 64-65