Classify your coin in three questions
First question: does the portrait wear a laurel wreath? If so, the coin dates from 1862 to 1868 and measures 17 mm. If not, it is a bare head, struck between 1854 and 1860.
Second question, for the bare head: how big is it? Around 14.4 mm, it is the small module of 1854-1855; around 16.7 mm, the large module introduced in 1855. Both weigh exactly the same, the second simply being wider and thinner.
Third question: which letter appears under the knot on the reverse? A means Paris, BB Strasbourg. The small module exists only with A, and the BB mint struck the type only from 1858.
Why the small module is uncommon
The decree of 12 January 1854 created a coin of about 14.4 mm, at first with a plain edge, then with a reeded one after a decree of July that year. The experiment was short-lived. In July 1855, 888,000 pieces were handed over for melting on the minister's decision, and the type lost legal tender status in 1859.
Out of some 4.5 million small modules struck, a sizeable share therefore vanished within months. The 1855 date, struck at under a million, is the scarcer of the two.
Laureate or bare: what the second portrait changes
The laureate portrait, engraved by Albert-Désiré Barre, was introduced in 1862 after a blank year: no gold 5 francs is dated 1861. The diameter grows to 17 mm. The reverse, however, keeps its laurel wreath, whereas the laureate 20 francs Napoleon III received the arms of the Empire.
Fewer laureate heads were made than large bare heads, and Strasbourg plays a bigger part: the BB mint struck every year from 1862 to 1868 and outdid Paris in both 1865 and 1867.
Neighbouring coins not to confuse
- Gold 10 francs of the same reign: the first module of 1854-1855 is 17 mm, like a laureate 5 francs, but weighs twice as much, about 3.22 g. Read the figure on the reverse, or see the page on the gold 10 francs.
- Silver 50 centimes: 18 mm, 2.5 g, white metal and the mark “50 C”.
- Silver 5 francs: no likeness in size, 37 mm for 25 g; see the silver 5 francs crown.
- Ceres gold 5 francs: struck from 1878 to 1889 under the Third Republic, with no emperor's portrait.
Examine, keep, beware
A ten-power loupe and a lamp held at an angle are enough. Wear first attacks the hair near the ear and the cheek on the bare head, the laurel leaves on the laureate head, then on the reverse the veins of the branches and the knot. Most family coins grade between Fine and Very Fine; an Extremely Fine piece keeps some original brightness near the letters. Each grade is set out on the grading page (in French).
Light and small, the coin often ended up as jewellery. Solder on the edge, flattened reeding, a filled hole or a re-polished area all point to a past mount. To rule out a copy, combine weighing, measuring the diameter for the type and checking the reeding and signature; the guide to fake coins goes further. And never rub the surface, as the guide on cleaning explains (both in French).