Art world agog as private hoard comes to light

The art world is preparing for the release of a treasure trove of new discoveries about historical works with the publication of a catalogue – nine years in the making – of Britain's biggest private art collection.

Later this month the Walker Art Gallery in Liverpool will showcase a handful of the discoveries from the Schorr Collection, created over 40 years by a chartered surveyor called David Lewis and his family.

The secrets have come to light over the years as the more than 400 paintings in the collection were cleaned and restored. But they have never been made public until now.

Among the revelations is the discovery of a sketch for two of El Greco's most famous paintings, of the Spanish town of Toledo. The Coronation of the Virgin was thought to be, primarily, a studio painting, but when it was cleaned a sketch of the town was found in the bottom-right corner, by El Greco himself.

Another painting, thought to be a copy of the Spanish master Velazquez, was shown to be the work of Delacroix when the full signature – "Delacroix after Velazquez" – was revealed.

Xanthe Brooke, the exhibition's curator, said: "In the case of Delacroix, we have a new painting in his oeuvre."

Mr Lewis said: " Often I am behind the conservator when the dirt or paint is removed. Of course there are times when nothing is revealed." But, he added, it was all "incredibly exciting".

'A Collector's Eye: Cranach to Pissarro' is at the Walker Art Gallery, Liverpool from 18 February

The Coronation of the Virgin

El Greco and his studio

When the painting was cleaned, conservators noticed a small landscape panorama in the corner of the canvas. This was found to be the town of Toledo in Spain, the subject of two of El Greco's most famous paintings – View of Toledo (1596-1600) and View and Plan of Toledo (1610) – considered among the greatest depictions of the night sky in Western art. The small landscape is by the master himself.

Assumption of the Virgin

Rubens

In 1611 Rubens made two oil sketches of the Assumption, to win a commission to paint the high altar of Antwerp Cathedral. One sketch is in Buckingham Palace. The Schorr Collection painting looks identical to the bottom half of the oil sketches. It was thought to be a later work, but wood-dating experts discovered the panel was of a soft wood found in southern Europe, where Rubens was in 1609, suggesting this is an earlier work than had been thought.

Moses and the Tablets of Law

Philippe de Champaigne

There are three versions of this painting: one in Milwaukee, one in St Petersburg, and one in the Schorr Collection. The one in the Milwaukee Art Museum was thought to have belonged to Cardinal Fesch, who was associated with Napoleon. But a newly discovered catalogue from 1860 reveals that the one in the Schorr Collection is, in fact, the one that belonged to the Cardinal.

Portrait of King Philip IV of Spain

Delacroix after Velazquez

This painting originally appeared to be signed just "Velazquez". When it was added to the Schorr Collection it was known as a copy, yet its owner David Lewis and his advisers were intrigued by its craftsmanship. The conundrum was solved when the full signature – "Delacroix après [after] Velazquez" – was revealed on cleaning. A fraudster had painted over part of the signature at some point, to make the work more valuable.