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

Here is the final tally for the '60s:

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 schillings 1963 KM#2889 (Hondo Boguss)
........Austria 10 schillings 1958 (Hondo Boguss)
........Curacao ½ guilder 1944 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)
60% Straits Settlements 20 cents 1927 KM#30b (Hondo Boguss)
........Sweden 20 ore 1907 KM#775 (triggersmob)
Also noted that the pergione of Milan circa 1400 was at around 66%, and that the Kutch 1/2 kori (Y-13) is at 61%. (Note: for some of the Kutch cois listed at 0.61 in Numista, KM has them at 0.601).

Time to post coins with the next 10%, 59 t0 50%.
I will open with the composition 58% (0.582), which was used for esterlins of Spanish Netherlands for 100 years (1612-1711). This one is KM#47 of the Duchy of Brabant (1612-1621).



And yes, that is a peacock and not an eagle

Another 50% silver coin - a 1920 Britisf florin. This is the year the silver fineness was reduced from 92.5% to 50% following the inflation and economic effects of World War I:

Excellent, tdziemia!

.500 - Peru 1 Sol 1931

50% Portugal

Wow! Nice additions, all!

I think I have one more composition to post later.

I like that it says so on the back of the coin!

Following up on an earlier coin for the 50-59% range...

Accordig to Gumowski's (1960) Poland catalog, there were three ordinances specifying the silver coins of Stanislaw August (1764-1795). In 1766, the 4 groschen coin, KM#185, was specified at 8 2/3 / 16th pure (0.542 or 54% as mentioned earlier). In 1787 the larger silver denominations were re-designed with a new bust of Stanislas, and the specifications for silver contents were lowered, in the case of the 4 groschen coin, KM#208.1, to 8 1/6 pure (51%).
KM has both of these 4 groschen coin at 55% The first could be a rounding error, but the second is wrong, as it misses the change to all the silver coins in 1787.

So, here is a 1787 4 groschen coin with the later portrait for 51%:

One of the series of 10-euro coins issued in 2011 to commemorate each region of France. These were only available at face value from post offices in the relevant region. 50% silver: