I regularly encounter interesting prospects, paintings or drawings which have been missed by the auctioneer and are severely undervalued. Soemtimes I list them here, often I share them with one of my contacts to try to buy them. Usually, this doesn't work out as I am not the only one noticing these, and others are less cautious in their estimates.
The latest one was yesterday, 28 March 2017, at Sotheby's. Finding a hidden gem at a small auction is nice, but finding one missed by the Sotheby experts is of course even nicer!
In a collection of "Sixteen Old Master drawings", estimated at £400 to £600, three drawings in particular caught my attention.
British Museum, from the same year, also from Don Quixote, which was clearly by the same hand and which was given to Christian Wilhelm Ernst Dietrich (also known as Dietricy) (1712-1774), versatile German artist. His drawings usually aren't extremely valuable, but then again they often are preparatory sketches, not the highly attractive finished work we see here.
I can't find any evidence that there ever was a published Don Quixote with these drawings, which would really be the icing on the cake. But even so, having two drawings of the same subject, with the same design of the character (including armour, shield, weapon, donkey, ...) and the same attribution (one by the BM, one on the drawing) makes it fairly certain that this is a genuine Dietrich drawing, and a very good one at that.
So my guess is that this drawing alone is the reason that this lot went for 10 times the estimate, and I hope that whoever bought it truly enjoys it as it is a small gem.