--- title: 'Metal teaware: tetsubin, silver, tin and copper' url: 'https://howtotea.me/teaware/materials/metal' markdown: 'https://howtotea.me/teaware/materials/metal.md' lang: en date: '2026-10-25' description: 'Tetsubin, silver, tin and copper tea vessels: how they are made, tetsubin versus tetsukyusu, what metal does to water, and how to avoid fakes.' --- # Metal teaware: tetsubin, silver, tin and copper Editors · October 25, 2026 · 11 min read Metal teaware is mostly for boiling water, less often for storing or brewing tea. A cast-iron tetsubin adds hundredths of a milligram of iron per liter, silver leaves water clean, tin keeps dry leaf well, and copper needs a tinned lining. ![A cast-iron tetsubin on its trivet and a pewter tea caddy](https://howtotea.me/images/c/o/v/e/r/cover-a1aa481f.webp) Illustration Metal Cast iron: tetsubin for water, enameled tetsukyusu for brewing Silver: for boiling water; tea is not brewed in it Tin: melts near 230 °C, never goes on a flame Copper: hammered kettle with a tinned interior Iron from a tetsubin: up to 0.03 mg/l (tap water, 30 min) Iron, silver, tin and copper found their way into tea along different roads. Iron and copper heated water over the fire. Silver did the same job, only more beautifully and at far greater cost. Tin was useless near a flame but kept dry leaf well. Each metal has its own job, and what people say about taste has to be kept apart from what has actually been measured. ## Tetsubin and tetsukyusu A tetsubin is a cast-iron kettle for water, with a spout, a lid and a bail handle arching over the body. The inside is bare. The finished kettle is fired on charcoal at 800 to 1,000 °C, which grows a film of magnetite, Fe₃O₄, that protects the iron from rust. Sources differ on how long: about 20 minutes according to the researcher Horie, about 30 minutes at roughly 900 °C according to the Japanese crafts registry. The outside is then brushed clean and tinted with urushi lacquer and iron acetate. The tetsubin grew out of the kama, the iron kettles of the [tea ceremony](https://howtotea.me/teaware/by-region/japan-and-korea/chanoyu-dogu). In 1633 the Nanbu clan moved its seat to Morioka and invited iron founders to the town, and in 1659 a kettle master arrived from Kyoto. Later the kettle shrank and gained a spout and a bail, and over about a hundred years its name shifted from "iron yakan" to tetsubin. A second center, Mizusawa, traces its lineage back to 11th-century founders. Nanbu ironware was recognized as a traditional craft on February 17, 1975, in the very first group to be designated. Nanbu molds are made from mane, a baked mold loam of sand and clay. The dotted arare pattern is pressed into the raw mold, about 2,000 impressions per kettle by Horie's count and 3,000 by the registry's. The iron is melted at 1,300 to 1,500 °C. Kyoto tetsubin of the late Edo and Meiji periods are a different thing altogether: small, thin-walled, lost-wax cast, often inlaid, with a bronze lid. They were made for [sencha](https://howtotea.me/brewing/methods/sencha-gyokuro) enthusiasts. A tetsukyusu looks the same but is enameled inside. Keep it off the flame, since the enamel flakes off when heated dry. You brew in it with water boiled in something else. From the outside the two are often impossible to tell apart, so check the label on the model. Some enameled pots are rated for direct heat, but they are the exception. Think of a tetsukyusu as an iron cousin of the [kyusu](https://howtotea.me/teaware/by-region/japan-and-korea/kyusu). ### Care Before first use, rinse the tetsubin, fill it to 80%, bring it to a boil over medium heat and pour the water out. Repeat two or three times, until the water stops clouding. After each boil, empty what is left into a thermos and let the kettle dry with the lid off on its own heat. Do not scrub the inside. Red spots appear over time, then a white film of yuaka, and the water stays clear. If you boil water daily, the film forms within a year to a year and a half. Wipe the outside of the hot kettle with a wrung-out cloth and it will take on a sheen. Rinse a tetsukyusu after brewing and dry it thoroughly, especially the spout and the underside of the lid: a drop of tea left for an hour or two will rust. ## Silver A silver kettle (ginbin in Japanese, yinhu 银壶 in Chinese) is for boiling water. Tea is not brewed in it, because flavor and compounds linger in the metal. An expensive ginbin is hammered from a single ingot, so the wall varies in thickness and is heavier at the base and the neck. A cheap one is spun on a lathe and comes out light and even. A hammered kettle has a thick neck, smooth on the inside, and sharp cones in its arare pattern. A spun one has a ridge on the inside of the neck and low, blunt cones. China's main center of hand silversmithing is Xinhua village in Heqing County, Yunnan, where smiths melt, roll, draw wire and chase. In 2014 the craft entered the fourth national list of intangible heritage. Its age is disputed: the registry says "more than 500 years", the local press "more than a thousand". Silver has long been prized in tea. Lu Yu in The Classic of Tea (8th century) calls a silver cauldron "the purest, but extravagant". Xu Cishu in Cha shu (1597) ranks silver first for a teapot and tin second.[1](#fn:1) Treat silver gently. Fill the kettle to 60 to 80%, or it will spit as it boils. Heat it on a ceramic electric hot plate, since an open flame yellows and blackens the metal and an ordinary ginbin will not heat on induction. Never boil it dry, and top it up with warm water, not cold. The tarnish is silver sulfide, from sulfur in the air. Mirror finishes can be cleaned with toothpaste, matte ones only with a cloth and a baking soda solution. ## Tin and copper Tin is soft, scratches even from cloth and melts near 230 °C (the same workshop gives 240 elsewhere), so it is not used for vessels that go on the fire. Lu Yu, Cai Xiang and Xu Cishu all weighed in on which metals suit the cauldron, the ewer and the pot, and Xu Cishu praised tin for the boiling pot: "its taste is not salty and not astringent". The sources do not say how Ming tin pots stood up to the flame. In Japan the main tin object for tea is the [tea caddy](https://howtotea.me/teaware/utensils/tea-caddies) with an inner lid, ground to fit so that moisture stays out and scent stays in. Osaka tin is cast, turned and polished with horsetail and mukunoki leaves, and the alloy is at least 97% tin. In China the Palace Museum holds over 200 tin pieces, mostly Qing teapots carved with poems and landscapes. Tin dislikes frost. Below -15 °C it can, rarely, turn into its gray form, "tin pest", and in a household freezer partial changes appeared within months. Wash tin with a soft sponge and mild detergent, no abrasives. Copper is the oldest material for water kettles, and the Japanese copper yakan is a direct ancestor of the tetsubin. A hammered kettle from Tsubame is raised from a single sheet, with about 15 trips to the annealing furnace along the way, and lined inside with a thin coat of tin. The Gyokusendo workshop was founded in 1816, and in 1873 its work was shown at the Vienna World's Fair. A kettle in the V&A collection has a body and lid of copper over 99.9% pure. ## What metal changes in water The evidence here is thinner than the marketing. **Iron.** A new Nanbu tetsubin filled with distilled water released 0.41 to 0.15 mg/l of iron, usually under 0.2 mg/l, and less with every use (a 2003 experiment funded by the producers' association). With tap water and 30 minutes of heating, the figure was no more than 0.03 mg/l (Hiratsuka et al., 2004). The Japanese reference intake for a woman aged 30 to 49 is 10.5 mg of iron a day, and a liter of such water covers about 2% of it. "A tetsubin cures anemia" is a myth. **pH and hardness.** In the same study, two Chinese cast-iron kettles raised tap-water pH from 7.00 to 9.40 and 9.00 in 30 minutes, and hardness from 19 to 44 and 53 mg/l. In four Japanese tetsubin, pH reached 7.76 to 8.35 and hardness 25 to 28 mg/l. The authors suspected that the jumps in pH and hardness, rather than the iron, are what spoil the tea. **Chlorine.** The maker Iwachu says the inside of the kettle absorbs chlorine from tap water. But 5 to 10 minutes of boiling with the lid ajar drives chlorine out of any water, so you do not need a tetsubin for that. For more on hardness and pH, see [water for tea](https://howtotea.me/brewing/basics/water) and [water chemistry](https://howtotea.me/science/water-and-extraction/water-chemistry). **Silver.** The WHO does not recommend silver for disinfecting drinking water and sets no formal limit, only a provisional reference value of 0.1 mg/l. In a Chinese experiment with beakers holding a silver flask, more silver leached the longer, hotter and more acidic the conditions, and in tea and hot acidic liquid it exceeded 0.05 mg/l, the Chinese drinking-water limit. That study did not test kettles, and there are no measurements for ginbin specifically. **Copper.** A 2007 experiment found that organic matter from tea, higher temperature and longer standing time all significantly raised the amount of soluble copper released from a copper teapot. The abstract gives no concentrations. It is an argument for a tinned lining. **Taste.** Stephane Erler of Tea Masters compared water from different kettles. He found tetsubin water "rounder and sweeter", with a faint iron note, and silver water "light and clean", the least altered of all. Hence his pairings: silver for light aromatic teas, greens and young sheng puer, tetsubin for roasted [oolongs](https://howtotea.me/teas/oolong) and aged puer. With [black tea](https://howtotea.me/teas/black) the difference is smaller. These are one practitioner's tastings, not blind panel tests. ## Choosing, and fakes Antique tetsubin get faked, and prices are all over the map. In 2012 an inlaid Ryubundo kettle by Yasunosuke sold in Shanghai for 977,500 yuan. A genuine Kibundo is lost-wax cast and has no seam "belt" around it. Japanese copies from the late Taisho and early Showa periods are sand cast, with a horizontal seam at the widest point. Modern copies are die cast in metal molds. Their vertical seam is ground down and painted over, the base has a sprue mark in the center with two gas holes beside it, and the inside is smooth and pore-free, often with artificial rust. Check the signatures on lid and body separately, because genuine Ryubundo lids turn up on bodies that are not their own. A repainted or polished antique loses value. For how to authenticate a piece, see [collecting teaware](https://howtotea.me/teaware/care-and-collecting/collecting). In 2023 a buyer in Shanghai paid 37,000 yuan for three "Japanese handmade" kettles "by a master". Examination showed serial lost-wax casting from a silicone mold and machine-engraved names. The Jiading district court ruled the sale fraudulent and awarded the buyer 151,000 yuan under the seller's own promise, "fake means four times the price". Silver is checked by its hallmark. The Chinese standard GB 11887-2012 lists fineness grades of 800, 925 and 990, stamped S925 or 银925, but it was written for jewelry. Tokyo silver is at least 925/1000. For coatings and alloys in tableware, see [teaware safety](https://howtotea.me/teaware/care-and-collecting/teaware-safety). For ordinary home use a plain [water kettle](https://howtotea.me/teaware/utensils/kettles) is still enough, and the samovar has an [article of its own](https://howtotea.me/teaware/by-region/europe-and-russia/samovar). ## Common questions Can you brew tea in a tetsubin? No. A tetsubin is bare iron inside and is only for boiling water. To brew, use a tetsukyusu, a cast-iron pot lined with enamel, or pour the boiled water into any other vessel. Does a tetsubin cure anemia? The data do not support that. With tap water a tetsubin releases no more than 0.03 mg/l of iron, a liter covers about 2% of the daily requirement, and tea also slows the absorption of non-heme iron. Why is the inside of my tetsubin rusty, and what do I do? A red interior under a film of scale is normal. If the water turns cloudy or smells, fill the kettle to 80%, add a teaspoon of sencha in a bag and simmer about 30 minutes. Tannins bind the iron. Notes 1. Sources disagree on how Lu Yu's sentence about the cauldron ends. Wikisource, Project Gutenberg and the Siku quanshu text read "in the end one comes to silver" (卒歸於銀), some modern editions "to iron" (卒歸於鐵). The collected sources do not settle which reading is original. [Wikisource, The Classic of Tea](https://zh.wikisource.org/wiki/%E8%8C%B6%E7%B6%93/%E5%9B%9B%E4%B9%8B%E5%99%A8). [↩](#fnref1:1) --- ## Navigation - Parent: [Teaware materials](https://howtotea.me/teaware/materials.md) - Previous: [Glass teaware](https://howtotea.me/teaware/materials/glass.md)