How Low (On Silver Content Below 70%) Can You Go?

The Brabant mite in late silver standard times was issued at 4 grains = 1.3% silver.

Then there's the Siberian copper issues (1765-1778) at 0.81% silver, which was the silver impurity content in Kolyvan copper as of 1763 or so; in 1768 the mint officials pointed out that due to better purification techniques the default silver impurity was down to 0.59%, and were apparently asked to continue maintaining the silver content artificially. Apparently the coins were XRF tested [warning: link goes to PDF attachment in Russian, apparently an article from a 2016 issue of a Russian numismatic journal] and the silver content was indeed held close to the standard 0.81% (in fact sometimes slightly higher) at least until 1778.
(In 1778 the officials pointed out further purification and were no longer asked to keep up; in any case production of separate Siberian coinage ended in 1781.)

I'm not aware of any coins with even less silver than that, though it would not surprise me much if they do exist.

My collecting interests are kind of narrow, so I was aware of the Brabant mite, but not any others. So it's neat to learn of the ancient types and SIberian coins.

To elaborate on the 1% types of Low Countries:

For Brabant, the mite of Philip the Good struck 1458-1467 (half the value of the 2% coin I posted) is 4 grains ("argent-le-roi"), 1.3% as pointed out by j1m. It was struck at two mints. Recent sales of each:
https://www.numisbids.com/n.php?lot...lot&sid=5729
https://www.numisbids.com/n.php?p=l...5729&lot=953
And one currently for sale on MA-Shops: https://www.ma-shops.com/cdma/item.php?id=1062471

For the next reign, Charles the Bold 1468-1477, there is a disconnect between the catalogs of de Witte (written 1896) and van Gelder & Hoc (1960) on the mite. de Witte first mentions a 2 mite coin struck at 10 grains and a 1 mite coin specified at 6 grains, then later says that in 1468 a 4 mite coin was added and the specifications were changed, but doesn't give details. Van Gelder & Hoc say the 10 grain coin was 4 mites, the 6 grain coin was 2 mites, and the 1 mite coin was struck at 3 grains (1%). This coin is also somewhat rare:
https://www.numisbids.com/n.php?lot...lot&sid=6212

I think the last coin struck in the Low Countries to a purity that rounds to 1% was the 2 mite of Charles V at 4 grains fine (0.014)
https://www.acsearch.info/search.html?id=1625309

I've only got one Tet II and it's a barbarous imitation, so not much use here.

Neat! According to j1m's comments, the silver in these was at first an impurity that would not meet our criteria, but became a specification by the date of this coin, so ....

Here is the current comprehensive list (maybe close to final?):

69% Poland ¼ thaler 1657 KM#A94 (tdziemia)
68% France 20 francs 1930s KM#879 (erafjel, Hondo Boguss)
67% France 30 sols 1792 KM#606 (ironhorse)
........Germany / Prussia 1/3 thaler KM#303 (spence)
65% Costa Rica 25 centimos 1924 KM#168 (NumisRob)
........Portugal 50 escudos 1971 KM#601 (triggersmob)
64% Austria 5, 10 schillings KM#2882, 2889 (Hondo Boguss)
........Curacao ½ guilder 1941 KM#44 (Hondo Boguss)
........Curacao 1/10 guilder 1944 KM#43 (january1may)
........Netherlands 5 cents 1859 KM#91 (spence)
........Netherlands 25 cents KM#164 (triggersmob)
63% Germany 5 marks 1958 KM#123.1 (mrwhatisit)
........Poland 2 gulden 1770 KM#186.2 (tdziemia)
62% Flanders 4 stuivers 1540 N#96940 (tdziemia)
61% India/Kutch 1 kori KM#Y-12 (oriole)
60% Straits Settlements 20 cents 1927 KM#30b (Hondo Boguss)
........Sweden 25 öre 1907 KM#775 (triggersmob)
Noted by j1m that the pegione of Milan circa 1400 was at around 66%.

59% Poland 2 zlote KM#C-123 (tdziemia)
58% Austria 20 kreuzer KM#1999 (paralyse)
.......Dutch Republic/Holland, 2 stuivers, KM#48 (spence)
.......Hungary, 20 krajcar, KM#432 (paralyse)
.......Spanish Netherlands/Brabant escalin KM#47 (tdziemia)
57% Nethelands 5 cents KM#52 (BCTokens)
........Liege escalin KM#165 (paralyse)
56% German States/Prussia 1/6 thaler KM#299 (spence)
.......German States/Oldenburg 28 stubuer KM#40(Jever) (paralyse)
55% Ceylon 10 cents KM#109a (oriole)
54% Poland 4 groszy 1767 KM#185 (tdziemia); KM has this at 55%
52% Austria ¼ Florin KM#2214 (oriole)
51% Poland 4 groschen 1787 KM#208.1 (tdziemia); KM has at 55%
50% Australia florin 1958 KM#60 (triggersmob)
........Canada 25 cents KM#62a, 68a (DBM)
........Egypt 2 quirsh 1944 KM#369 (Hondo Boguss)
........France 10 euros 2011 (NumisRob)
........German States/Bavaria 20 kreuzer KM#549.1(paralyse)
........Great Britain florin KM#817a, crown KM#836 (NumisRob)
........Great Britain halfcrown KM#818.2 (paralyse)
........Great Britain 3p KM#848, 6p & shilling KM#852, 853 (Hondo Boguss)
........India ½ rupee 1945 KM#552 (Hondo Boguss)
........New Zealand ½ Crown 1935 KM#5 (Hondo Boguss)
........Peru 1 sol 1931 KM#218.2 (Hondo Boguss)
........Poland 1 gulden 1664 KM#120 (tdziemia, paralyse)
........Portugal 1000 escudos KM#731, 10 euros 2010 (hfjacinto)
........Russia 10 kopeks KM#Y20a (paralyse)
........South Africa 50 cents KM#62 (Hondo Boguss)
........USSR 10, 15, 20 kopeks KM#Y80-82 (january1may)
Noted that the 1/6 talara coin of the Duchy of Warsaw, KM#C85 under Poland is 53%.

49% German States/Saxony-Albertine 1/12 thaler KM#638 (paralyse)
48% Burgundian Netherlands/Brabant 2 gros N#95425 (tdziemia)
.......France, blanc Charles VI (1385-1389) (erafjel)
47% Turkey/Ottoman yuzluk KM#507 (oriole)
46% Duchy of Brabant ½ real N#44048 (tdziemia)
45% Poland 6 groschen KM#42 (tdziemia)
44% German States/Hamburg doppelschilling KM#419 (spence)
.......German States/Hamburg 4 schilling (KM#359.1) and 8 schilling KM#367 (paralyse)
.......German States/Prussia 1/12 thaler KM#298 (paralyse)
42% Mexico 50 centavos KM#448 (ariette)
41% Burgundian Netherlands/Brabant 2 gros N#104038 (tdziemia)
40% Burgundian Netherlands/Flanders, briquet N#248787 (tdziemia)
.......France, blanc Charles VII N#4633 (erafjel)
.......French Indochina 10 cents KM#14 (erafjel)
.......Sweden I krone KM#814 (paralyse)
.......Sweden 5 kronor KM#839 (triggersmob)
.......U.S. Eisenhower dollar (jbuck, paralyse, kbbpll)
.......U.S. Kennedy half (paralyse)
Noted by january1may that medieval Brabant 2 gros coin N#309707 is 43%.

38% German States/Baden 6 kreuzer KM#140 (paralyse)
........German States/Nassau 6 kreuzer KM#53 (paralyse)
........German States/Prussia 2 ½ groschen KM#486 (mrwhatisit)
........Lithuania ½ groat Alexander N#31088, 343561 (DBM, january1may)
........Lithuania ½ groat Sigismund I N#63424, 130413 (january1may, DBM)
........Lithuania ½ groat Sigismund II N#35047, 104468 (tdziemia)
........Poland grosz, Torun N# 182407 (paralyse)
........Sweden 1/24 Riksdaler KM#522 (paralyse)
37% Germany/Anhalt-Bernburg 1/24 thaler KM#79 (paralyse)
........Poland 1 groat KM#163 (tdziemia)
36% Lithuania groat KM#10 (tdziemia)
35% Dominican Republic ½ peso KM#15 (ariette)
........Finland 1 markka KM# 49 (triggersmob)
........German States/Saxe-Meiningen 6 kreuzer KM#134 (paralyse)
........U.S. Jefferson War Nickel (Hondo Boguss, jbuck, paralyse)
34% Lithuanian groat 1566 N#46216 (tdziemia)
33% France 10 euro Le Mans KM#3229 (Numisrob)
........German States/Baden 3 kreuzer KM#211 (spence)
........German States/Bavaria 3 kreuzer KM#800 (paralyse)
........German States/Frankfurt 3 kreuzer KM#373 (paralyse)
........German States/Wurttemburg 3, 6 kreuzer KM#572, 577 (paralyse)
32% France, Charles VIII dizain N#34529 (erafjel)
31% German States/Mecklenberg-Schwein schilling KM#273 (paralyse)
........German States/Prussia 6 groscher KM#A297 (spence)
........German States/Prussia 1/24 thaler KM#296 (paralyse)
........Italy/Papal States-Bologna muraiola KM#146? (january1may)
........Silesia/Schweidnitz ½ groat N#65413 (tdziemia)
30% France denier tournois Louis IX N#42076 (erafjel)
........Mexico 25, 50 centavos, peso KM#443, 449, 457 (Hondo Boguss)
Noted by @paralyse that some 18th century Venetian coins KM#502, 504, 545, 575 are at 39%.

29% Poland 6 groszy KM#155 (tdziemia)
28% County of Flanders 1 groot N#98102 (tdziemia)
26% County of Holland 1 groot N#98269 (tdziemia)
25% East Africa 1 shilling KM#28 (oriole)
.......East Africa 1/2 shilling KM#20 (NumisRob)
.......German States/Hamburg sechsling KM#585 (paralyse)
.......Somalia 1 somalo KM#5 (mrwhatisit)
24% France/Brittany liard 1492-1498 N#178499 (erafjel)
23% Poland Elbing schilling N#107714 (tdziemia)
22% German States/Hanover 1 groschen KM#236 (spence, paralyse)
........German States/Saxe-Weimar-Eisenach 1/2 & 1 gr KM#198, 199 (paralyse)
........Lithuania 1 denar N# 46192, 175323 (january1may)
........Lithuania 2 denars N#36694, (tdziemia)
........Poland 1 denar #175270 (january1may)
........Turkey/Ottoman 5 kurus KM#591 (mrwhatisit)
21% France 30 deniers KM#378.1 (january1may)
........French Guiana 2 sous KM#1 (Hondo Boguss)
........German States/Mecklenberg-Schwerin 1/48thaler KM#311 (paralyse)
20% German States/Westphalia 10 centimes KM#96 (paralyse)
Noted by erafjel that there are some 27% coins from medieval France.

19% Poland 5 groszy KM#C96.3 (spence)
........Poland 10 groszy KM#C84 (tdziemia, oriole)
18% France/Dauphine Charles V liard (erafjel)
17% Germany/Bavaria 1 kreuzer KM#858 (paralyse)
........Germany/Bremen 1 groten KM#213 (paralyse)
........Germany/Frankfurt 1 kreuzer 1859 (paralyse)
........Lithuania solidus/schilling (tdziemia)
........* Lorraine liard N#59724 (erafjel). Probable but not confirmed.
16% Poland-Lithuania Stefan Batory schilling N#96442 (tdziemia)
........Poland-Lithuania Sigismund III schilling N# 96677 (spence)
13%* Sweden ½ ore N# 31345 (january1may); listed at 14% on Numista
13% France Henry III liard N#43704 (erafjel)
.......Lithuania schilling/solidus KM#41 (tdziemia)
11% Italy/Venice tornesello N#76361 (january1may)
10% Mexico 1 peso KM#459 (Hondo Boguss, paralyse)
.......France/Lorraine 2 deniers 1581 (tdziemia). Probably but not confirmed
Noted that some medieval Low Countries 1/4 gros/groots are at 14% and 15%.

9% Lithuania 2 denars KM#15 (tdziemia)
.......Poland Gdansk solidus/Schilling N#96806 (tdziemia)
8% Cyprus (Venetian) carzia N#127028 (january1may)
7% France Francois I denier tournois (#39083 (erafjel)
6% * Poland 1 solidus/schilling Torun N#182131 (tdziemia), probable not confirmed
5% France Louis XI obol tournois N#65414 (erafjel)
.......Roman Empire, Diocletian antoninianus (paralyse)
4% France/Hainaut 2 deniers #95706 (tdziemia)
3% County of Flanders 2 mites N#126945 (tdziemia)
2% Duchy of Brabant 2 mites N#108934 (tdziemia)
1% Russia/Siberia 5 kopeks KM#C-5 (oriole)

Of 69 possible compositions (according to our rules), we've accounted for 61, missing only these:
66%, 53%, 43%, 39%, 27%, 15%, 14% (though we found one Numista has, but probably erroneously), and 6% (where we only have a "probable").
(and I started out thinking that 30 might be a stretch!).

Two weeks ago I lost track of already having a 2% coin, and picked up this one that came in the mail today (same shipment as my 46% and 26% coins for which I posted the seller's photos).
Duchy of Brabant, Charles V undated 2 mites (1524-1528) N#74408, 2.4% silver.

Way back at the top of page 3 when we were looking for coins in the 60-70% range, @j1m found a Milan coin listed on Numista:




By accident, while researching something else, I ran across the source. Medieval European Coinage, Volume 12 on northern Italy, says this on page 449 (edited for brevity):
Along with the new design of the grossi struck under Bernabo and Galeazzo, the denomnation also changed. It was no longer worth two soldi ... but only one and a half. The weight was reduced accordingly from 2.9 to 2.5-2.6 g. and the fineness decreased from 90% silver to only 66%. (Gnechhi and Gnecchi 1884).

Later the author comments that this weight and fineness reduction lasted "through to the fifteenth century." I cannot find any reference to additional debasements, so I doubt that the grosso pegione changed in fineness later in the reign.
He also attributes the reduction to a reaction to introduction of debased types (blancs?) in France under Philip VI and John II in the mid 14th century.

There seems to have been a number of Galeazzos ruling Milan, but if it is Galeazzo II followed by Bernabo, we are talking 1355-1385. That fits with the rule of French king John II, who during the decade 1351-1361 debased and partially restored the money (just to soon be followed by a new debasement) 14 times, with the overall tendency falling. It was done to all silver/billon, including gros and blancs.