20g Silver Bar (various manufacturers)
€81.03
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20 g Silver Bars
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20g Silver Bar Heraeus
€81.08
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20g Silver Bar Umicore
€81.11
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Where minting stops.
Silver bars range from a few grams to about 31 kilograms. Between 10 grams and 15 kilograms, the small ones are usually minted and the large ones cast. Where one stops and the other begins, each house decides for itself.
Umicore mints its silver bars from 10 to 100 grams. From 250 grams on, the house casts them, right up to 15 kilograms.
At Heraeus, the line falls in the same place. There, the ounce and 100 grams are minted, while 250 and 500 grams and 1, 5 and 15 kilograms are cast.
Other houses draw the line somewhere else entirely. Heimerle + Meule already casts the ounce, a small square with sides of 23.5 millimetres. Valcambi still mints the kilo, 130 millimetres long and 11.2 millimetres thick.
The larger the bar, the more likely it is cast.
Sizes according to the makers, for Heraeus only the sizes the house itself lists; the minted ounce from Heimerle + Meule according to its bar in the shop. On the axis, it is as far from 10 to 100 grams as from 100 grams to 1 kilogram.
Umicore 250 g silver barUmicore 250 gUmicore’s smallest cast barSmallest cast barFineness 999/1,000999/1,000
Why molten silver shuns the air.
When pure silver melts, it takes up oxygen from the air. As it solidifies, the oxygen escapes again, and that can happen violently. Old encyclopaedias call it spitting.
“When melted in contact with air, pure silver absorbs a great deal of oxygen, which, however, escapes at the moment of solidification …”
Pierer’s Universal‑Lexikon, volume 16, 1863, entry “Spratzen”, translated
In doing so, the oxygen breaks through the crust that has already set and drives out the silver that is still liquid, into a spongy mass from which beads of silver leap. That is how Pierer’s encyclopaedia describes it.
The chemist Gay‑Lussac caught the oxygen under a bell jar filled with water. He obtained twenty to thirty times the volume of the silver, Pierer reports. In 1911, the Encyclopaedia Britannica gives twenty times. These are figures from encyclopaedias of 1863 and 1911, not present-day measurements.
The remedy is given in the same article: stir while the silver solidifies, “but best of all” sprinkle charcoal powder on it before it sets. According to Pierer, silver with 1 to 2 percent copper does not spit, but pure silver does.
The oxygen is not entirely out of the picture. When a refinery on the London list assays its silver with a spectrograph today, oxygen and nitrogen expressly count as silver.
Diagram after the description in Pierer’s Universal‑Lexikon of 1863, not to scale.
Heimerle + Meule 1 kg silver barHeimerle + Meule 1 kgCastCastFineness 999.9/1,000999.9/1,000
The dip in the top face.
Silver contracts strongly as it solidifies, the Meyers encyclopaedia of 1909 writes. On a cast bar, this shows on top: the top face can sink slightly in the middle, and rings from cooling can appear as well.
“Excessive shrinkage (i.e. the concavity of the top face of the Bar and any concentric cooling rings) must not significantly affect the clarity of the Bar marks or the safe stacking of the Bars.”
LBMA, Good Delivery Rules, Technical Specifications, section 2.1.4
The LBMA is the association of the London precious metals market. Its rules are written for the large bars of this market. They show what happens when silver is cast.
Silver has rules of its own there. A little hammering of the surface is allowed; for gold, at most the smoothing of a sharp burr. And closed moulds have been banned for silver since 2008, mainly because hidden cavities can form in them.
Cast bars are wider at the top than at the bottom. On the 15‑kilogram bar from Umicore, the top face measures about 235 by 100 millimetres and the bottom 210 by 80, with a height of 75 millimetres. For its silver bars, the LBMA requires a slope of 5 to 15 degrees, so that they are easy to grip.
Calculated from Umicore’s dimensions, the sides of its cast bars slope at about 6 to 10 degrees.
A cast bar shows on its top face how it solidified.
Dimensions from Umicore. In gold, the top face, the dip in it only suggested: its depth has not been measured. The slope is calculated from the top and bottom widths and the height.
Umicore 15 kg silver barUmicore 15 kgCastCastFineness 999/1,000999/1,000
Silver is assayed differently from gold.
For gold, the LBMA requires its referee laboratory to carry out the fire assay, at least six times. For silver, the laboratory measures what is not silver and subtracts it from 1,000 parts.
“In the case of silver, the Referee will normally use one or other spectrographic analysis method and determine the silver assay by difference (with dissolved gases such as oxygen counting as silver).”
LBMA, Good Delivery List Rules, January 2026, Annex D, section 2.3
These are the rules for the refineries on the London list. They show how differently the two metals are assayed.
For a long time, silver was assayed in fire, in small dishes called cupels. In 1832, the French mint commission published instructions by Gay‑Lussac, the same man who had caught the oxygen in silver. After that, it could also be done “by the wet way”: the silver is precipitated with a solution of common salt instead of being assayed in fire in the cupel.
In 1874, Jacob Volhard described another wet method, with thiocyanate instead of common salt.
The common salt assay lives on in the standards. ISO 13756 determines silver in jewellery and precious metals with sodium or potassium chloride, ISO 11427 with potassium bromide, both today in the edition of 2024 and for silver contents of 100 to 999 parts per thousand. For higher contents, both name spectroscopy by difference.
With silver, the rest is what counts: 1,000 parts minus everything foreign.
According to the LBMA rules of January 2026. The foreign share is drawn greatly enlarged.
Heraeus 1 kg silver barHeraeus 1 kgCastCastFineness 999.9/1,000999.9/1,000
Three pounds, stamped in.
Stamping the weight onto the bar is an old practice. The silver treasure of Kaiseraugst in Switzerland includes a bar from shortly after AD 350. Punched into it is P III, three Roman pounds.
The bar measures 12.3 by 7.8 centimetres and is 1 centimetre thick. It weighs 947.8 grams, which corresponds to three Roman pounds.
Beside it are two small stamps reading GRONOPI, probably the name of the official in charge, and a round stamp with the bust and name of the Emperor Magnentius.
A kilo bar of today weighs almost the same, yet has a different shape. The cast kilo bar from Heraeus measures 111 by 51 millimetres and is 21 millimetres thick, more than twice as thick as the Roman bar.
Much older still is a silver bar with Hittite hieroglyphs in the Metropolitan Museum in New York, from the 14th to 13th century BC.
More than 1,650 years ago, the weight was already on the bar.
Dimensions: Augusta Raurica, Augster Blätter zur Römerzeit 10, and the makers. All three from above at the same scale, the kilo bars as product photos from the shop, the Roman bar drawn as an outline to its dimensions.
Umicore 1 kg silver barUmicore 1 kgOn the bar: 1000 g1000 gFineness 999/1,000999/1,000
Sources: Umicore, website on its silver bars; Heraeus, product pages of the silver bars; Heimerle + Meule, investment poster 2025; Valcambi, websites “Minted bars” and “Cast bars”; Pierer’s Universal‑Lexikon, volume 16, 1863, “Spratzen”; Meyers Großes Konversations‑Lexikon, 6th edition, volume 18, Leipzig 1909, “Silber”; Encyclopaedia Britannica, 1911, “Silver”; LBMA, Good Delivery List Rules, January 2026 (sections 2.1 and Annex D), and Good Delivery Rules, Technical Specifications; Gay‑Lussac, “Instruction sur l’essai des matières d’argent par la voie humide”, Paris 1832, according to the catalogue of the Wellcome Collection and the Dictionary of Scientific Biography; J. Volhard, Journal für praktische Chemie 9, 1874; ISO 13756 and ISO 11427, 2024 edition; Augusta Raurica, Augster Blätter zur Römerzeit 10; product photos from the shop; all accessed in October 2026. Images: silver bar with Hittite hieroglyphs, The Metropolitan Museum of Art, New York, 1989.281.16, public domain; cupels and cupel mould, woodcut from Lazarus Ercker’s book on assaying, printed in 1629, Deutsche Fotothek, public domain; seven bars from the shop’s product photos on a background generated with AI; mould and charcoal powder generated with AI.
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