Pewter ialah sejenis aloi logam tertempaan yang lazimnya terdiri daripada 85–99 peratus kandungan timah, dan selebihnya terdiri daripada tembaga, antimoni, bismut dan plumbum. Tembaga dan antimoni bertindak sebagai pengeras, manakala plumbum sering digunakan untuk menghasilkan piuter bergred rendah yang menampakkan sedikit warna kebiruan. Takat lebur piuter agak rendah, iaitu sekitar 170–230 °C, bergantung pada campuran logamnya.
Penggunaan terawal piuter adalah pada awal Zaman Gangsa di Timur Dekat. Hasil piuter terawal yang dijumpai hingga kini diperoleh daripada sebuah makam Mesir Purba dari 1450 SM.
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Juzuk piuter mula dikawal oleh persatuan bandar di Perancis pada abad ke-12. Pada abad ke-15, syarikat Worshipful Company of Pewterers mengawal juzuk piuter di England. Syarikat ini pada mulanya ada dua gred piuter, diikuti gred ketiga pada abad ke-16. Jenis pertama, iaitu fine metal yang terdiri daripada timah dan secukup tembaga yang boleh diserap (sekitar 1%), digunakan untuk penghasilan pinggan mangkuk. Jenis kedua, iaitu trifling metal atau trifle yang terbentuk daripada fine metal dengan kira-kira 4% plumbum, digunakan untuk membuat barang cembung (teko, tekoan kopi, mangkuk gula dsb). Jenis piuter yang terakhir pula, iaitu lay atau ley metal yang terdiri daripada timah dengan 15% plumbum, digunakan untuk barangan yang tidak bersentuhan dengan makanan atau minuman. Ketiga-tiga aloi ini digunakan tanpa banyak perubahan sehingga abad ke-20.
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Kini, piuter mesti mengandungi sekurang-kurangnya 90% timah dan dialoikan dengan tembaga, antimoni, atau bismuth, barulah menjadi piuter, sementara plumbum tidak diterima sebagai unsur pengaloian lagi.
Aloi tuangan Eropah biasanya mengandungi 94% timah, 1% tembaga, dan 5% antimoni. Helaian piuter Eropah mengandungi 92% timah, 2% tembaga, dan 6% antimoni. Piuter Asia yang pengeluarannya tertumpu di Malaysia, Singapura, dan Thailand, mengandungi peratusan kandungan timah yang lebih tinggi, iaitu lazimnya 97.5% timah, 1% tembaga, dan 1.5% antimoni, jadi aloi ini lebih lembut sedikit berbanding piuter Eropah.
Barangan hasil piuter sering ditemui dalam gereja. Piuter digunakan dengan meluas sejak Zaman Pertengahan hinggalah berkembangnya penghasilan kaca pada abad ke-18 dan ke-19. Piuter merupakan bahan pembuatan pinggan mangkuk meja terutama sebelum bangkitnya hasil porselin. Ramai yang menyangka bahawa penggunaan hasil piuter berplumbum ada kena mengena dengan kecurigaan orang ramai terhadap pemakanan tomato di Eropah Utara pada abad ke-16, tetapi tanggapan ini tiada kebenarannya.
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. Pengeluaran hasil kaca secara besar-besaran telah menyebabkan piuter terpaksa memberi laluan kepada kaca untuk kegunaan seharian. Namun begitu, bahan artifak piuter masih dihasilkan, terutamanya sebagai barang hiasan atau cenderahati. Piuter juga digunakan di Asia Timur, tetapi di Rom Purba pula jarang sekali ditemui.which is rich in kaolinite or hydrated alumina silicate. Red clay consists of rubber particles. Each rubber particle is made up of
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AKTIVITI selepas beberapa lama./ The people in the affected area either will be killed instantly by the atomic bomb, or for those
Work in pairs. A student is required to relax on a chair. Take the pulse rate reading at rest before the activitiesPewter is a tin alloy. According to ASTM standards, it contains at least 90% tin. Modern pewter also contains antimony (5-10%), copper (2% or less), and sometimes bismuth and silver. Old pewter contains tin, alloyed with lead and copper. Antimony, copper, and lead make pewter harder than pure tin and give the metal a blue tint. Polished pewter is a blue-silver metal, resembling platinum. However, pewter rapidly oxidizes to a gray patina (antimony pewter) or nearly black patina (lead pewter). People have used pewter to make practical and decorative items since the Bronze Age (c. 1450 BC).
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Pewter that contains lead is not safe for use with food. Acidic foods and beverages, such as wine, fruit juice, tomatoes, and salad dressings, leach lead vigorously from the alloy. But, even neutral substances, like water, absorb lead from the metal. Jewelry made from pewter that contains lead also poses a health risk, as some lead may be absorbed through skin. Children who wear jewelry may place it in their mouths. Pewter items that contain lead may be displayed as decorative items, but shouldn’t be handled or used.
Lead-free pewter is safe for use with food and for jewelry. Elemental antimony (as in an alloy) does not pose a health risk, but is unclear whether the metalloid absorbs across skin. Antimony compounds are toxic, so it’s best to use polished pewter in contact with food, avoiding any oxidation products. The metal isn’t the best choice for long-term food or beverage storage. Pewter is unsuitable for cookware because it has a relatively low melting point [170–230°C (338–446°F)]. Do not use pewter in the oven or microwave.
Two quick ways to check for lead are to look at the color of the metal patina (very dark oxidation usually indicates lead) or examine the mark left from rubbing the pewter item on a sheet of paper (heavy and dark mark indicates lead). Another method involves dipping the item into vinegar and checking for a white stain, theoretically indicating lead acetate or lead carbonate. However, these “tests” aren’t reliable.
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The best way to test for lead in pewter is using a lead test kit from the hardware store. This involves swabbing an area of metal with test chemicals and looking for a color change. For most kits, pink or red indicate lead. After testing, rinse the pewter item with soap and water. The Canadian Conservation Institute uses Plumbtesmo 90602 test spots, but warns tellurium, cadmium, silver, and strontium can interfere with the test. In other words, if any of these elements occur in the pewter, it can test positive for lead even if the alloy doesn’t contain it.
The natural darkening over time adds beauty and character to a piece. Polishing old pewter typically decreases its value. However, if pewter becomes soiled (or you just like it shiny), simply wash it with warm, soap water and dry it with a soft cloth. Avoid using abrasives, as the metal is soft and easily scratched. Do not wash pewter in the dishwasher.
Pewter is not magnetic. None of the elements found in the alloy are magnetic, regardless of whether or not pewter contains lead. Magnetism may be used to distinguish pewter from iron-based alloys, but not from gold, silver, sterling silver, or platinum (all non-magnetic).
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“Mexican pewter” is not actually pewter because it does not contain tin. It is an aluminum alloy, typically made by recycling aluminum cans. It is used to make decorative items and tableware that resemble pewter.
