"Van Poelenburgh", "Van Cuylenborch", what's the difference?

Galerie Moderne, from Belgium, sells on 16 October 2018 an "attributed to Cornelis van Poelenburgh" Antique ruins with Diana, on oil on panel estimated at 3,000 to 5,000 Euro.

The attribution to Van Poelenburgh (1594-1667) is understandable, he is known for similar nudes in landscapes, but they are usually situated in the open, with rather different colouring. These cave or grotto scenes in brown are much more typical of the work of Abraham van Cuylenborch (1620-1658), and this fits nicely in with his known works.

The above  "Nymphs in a grotto" from the Statens Museum for Kunst in Copenhagen has the exact same left side of the painting, and seems to be comparable in quality (but the image is too small to be certain).

The work for sale is actually very well executed, and is at least a good workshop version.

A lot of paintings attributed to Cuylenborch (but of varying quality) appear at auction though, and many remain unsold, so the market for his work is not very strong at the moment. Despite the real quality here, and the direct link to a museum piece to strengthen the attribution, it may struggle to get much more than the estimate. Which is a shame really, as it should be worth 10,000 Euro.

"Dutch painter" is a painting from the workshop of Abraham van Cuylenborch

Wannenes, from Italy, sells on 31 May 2017 as lot 533 a "Dutch painter, 18th-19th century" Bathing nymphs estimated at 500 to 800 Euro.

Another, at first sight better painted version of the work, but with about the same dimensions, was for sale at Dorotheum in 2016 with an estimate of 6,000 to 7,000 Euro. There it was called a Bath of Diana. It wasn't sold.

The work for sale lacks the same quality, but I wonder whether this is due to some poor overpainting. Normally, a poorer copy wouldn't have such rather greyed out but otherwise good figures in the background, I think. The second and fourth picture show the same details in the Dorotheum version.

Anoother version was available from Sotheby's (2016, est. 10,000 Euro, unsold) Other, simlilar works by Cuylenborch usually fetch around 4,000 to 5,000 Euro.

Considering all this, the estimate for this one seems to be too low and a 1,500 Euro estimate may be more correct if you are willing to take the gamble that cleanup will indeed reveal more detail and quality.