portrait of a young man, and a portrait of a lady.
Both works are dated, but in Italian, not in French, which might have been an indication that they were not "Frecnh school" but Italian. The man is dated "i 24 dicembre 1618", the woman "i 35 Aprile 1619". Since, even in those days, April didn't have 35 days, I presume "i 24" and "i 35" are sequential numbers, or else I am misreading something. As the "1"s in the years are also dotted, it may well be "124" and "135".
This time I was lucky though, and I found a lot of other drawings of similar style and quality which use the same dating and numbering system (and handwriting). The other drawings are all of similar dimensions as well.
Drawing from the Lille catalogueOttavio Leoni (1578-1630) is an Italian artist best known for his portrait drawings. An exhibition catalogue from the Museum in Lille has some more information on this artist, and explains "Most of Leoni's portrait drawings are inscribed with the month and year in which they were executed, as well as a number. These numbers are sequential, with the series beginning in 1615 and ending in 1629". It further explains that most of his pre-1620 drawings were in black chalk only, with post-1620 drawings also using red chalk.
This book on Bernini also discusses Leoni, describing his portraits as an "extraordinary series of drawings" and Leoni as "unequaled in sketch portraits"
Portraits which seal the attribution include:
*this 1620 portrait, number 154, which has the same mark (a reversed P, some watermark perhaps?) to the right of the head (which is very similar to the sitter of the work for sale), and which has at the bottom the same mark of an O with a cross or X below it
Antiques and Fine Art Magazine make it clear that Number 137 is dated April 1619, which matches exactly with our number 135 from the same month.
In total, there were some 400 numbered drawings, which regularly appear on the art market (and what a fabulous collection target to reassemble as many of these as possible!). The prices vary, Sotheby's sold one in 2015 for £10,000, and one for $25,000 in 2008. A portrait from early 1618 was sold at Christie's Paris in 2014 for 4,750 Euro.
The very cheapest I have found for a Leoni with the number and date was $2,500, but usually these fetch around 5,000 Euro each. And if you are really lucky and can find the identification on the back, and it turns out to be someone really important, then the sky is the limit
UPDATE: not sold, perhaps not enough people recognised this? Perhaps I should have gone for them myself...
UPDATE 2: apparently there was an error at the auction site originally, as it now says that they were sold for 12,000 Euro and 14,000 Euro, which is much more logical.