How is an artwork appraised?

Old Master paintings

‘Artists’ signatures became particularly prevalent during the early Renaissance in roughly the 15th century,’ explains Maja Markovic, Head of Day Sale in the Old Master Paintings department at Christie’s. ‘It was at this point that they started to assert their individual creativity and autonomy from guild systems by painting a name, symbol or monogram on the work, displaying their pride in their creation.’

A signature can do more than simply help to confirm the authorship of a work. The style of the signature can be checked against those in the artist’s catalogue raisonné while, says Markovic, ‘a signature can also help narrow down the date of a work based on its evolution over time’.

However, it’s not always so straightforward. Artists with large workshops would often sign works that had been partially, or sometimes wholly painted by their assistants, as long as it met their standards of quality.

Followers of artists were also known to forge the signatures of more established masters, and centuries later signatures were sometimes added by those looking to make a profit. ‘It’s important to make sure that the signature is in keeping with the artist’s known way of signing, and that it sits correctly with the original paint — not on top of the craquelure,’ Markovic stresses. ‘These factors can drastically alter a work’s value.’

In the example shown above, David Teniers the Younger helpfully signed the lower-left corner of the painting on copper, and included the year he finished the work.

‘He then also painted a dated print of his self-portrait in the background, as a way of further signing the work,’ Markovic reveals. ‘This shows it was clearly a work he was very proud of.’ In 2019, the painting sold for £4,746,250 at Christie’s — a new world record for the artist.

Chinese paintings

Over the past 1,500 years of Chinese painting and calligraphy, reproducing works — and even the signatures ­— of past masters has been a cornerstone of an artist’s development, explains Dr Malcolm McNeill, a specialist in Christie’s Chinese Paintings department. As a result, dating and authenticating works can be tricky.

However, there are plenty of clues available to a specialist’s trained eye. ‘For most artists, the habitual movement of the brush when writing calligraphy or a signature becomes a rapid, automatic motion,’ O'Neill says. ‘Copyists are inevitably slower and less confident, and you can see when their brush halts.’

Artists’ seals are equally complex. ‘Every seal has small nicks and indentations visible under close examination,’ he explains. ‘Reproducing these perfectly is near impossible,’ he adds. Christie’s specialists are trained to recognise these tell-tale signs, which are invaluable when appraising a Chinese painting.

In 2019 Christie’s offered a a nine-metre long, 16th-century handscroll by the artist Wen Zhengming, which he had signed, dated and stamped with 11 of his personal seals. ‘Poems in Large Running Script  meets the gold standard in authenticity, and its consignment directly from the Chokaido Museum in Japan underscored its incredible provenance,’ says McNeill. The painting went on to realise HKD $83,227,500 — more than 16 times its low estimate.

Early European sculpture

‘When assessing a sculpture I turn it upside down and examine the area that the artist didn’t mean to be seen. This helps me tell how, when and where it was made,’ reveals Milo Dickinson, Head of the Early European Sculpture & Works of Art department at Christie’s. ‘If it’s a bronze sculpture I’m looking for a cavity, which could suggest it was cast using the early lost-wax technique. Fifteenth-century bronzes made this way, for example, are much thicker than 18th-century examples, because the casting process was refined over the years.’

The next step is to look for areas that might be less oxidised, and therefore without a patina. ‘Here it is easier to for me determine the metal’s alloy,’ says Dickinson, ‘which can help identify the sculpture’s origin, and even the artist.’

In 2014 Dickinson was asked to examine a bronze statue of Venus, which was thought to have been cast by the Renaissance artist Antonio Susini. Turning it over revealed a hole of uneven thickness which, the specialist explains, suggested it had been cast using the lost wax technique in the 16th century. 

‘Also, the internal bronze’s original light-reddish colour meant it had a high copper content, typical of Florentine Renaissance foundries,’ says Dickinson. ‘This evidence supported our attribution, and when the sculpture came to auction it realised £1,058,500.’

‘One of the first things I do is hold a print up to the light so I can determine what kind of paper it is printed on,’ explains Alexandra Gill, Senior Specialist in Christie’s Prints & Multiples department in London. ‘From the 15th century, “laid paper” was used in Europe. Made from fine, linen pulp, it is recognisable by its vertical and horizontal lines, made by the wire sieves used to press each sheet.’

After the 1750s ‘wove paper’ was introduced, which was created using wood pulp and has a denser and a more uniform texture — ‘the same type of paper we use today,’ says Gill. ‘If the paper doesn’t seem right for the period of the work, alarm bells ring.’

Holding the paper to the light also helps to reveal watermarks — colourless designs impressed into the sheet as it was made. 

‘We know, for instance, that in the 1630s Rembrandt sometimes used paper with a watermark depicting a double-headed eagle with a crown,’ says Gill. ‘Also, to take another example, that between 1938 and 1939 Picasso published his set of 100 etchings known as the Vollard Suite on paper specially commissioned from the Montval factory near Paris, which featured his own and Vollard’s signatures as the watermarks,’ Gill says. ‘So catalogues of which watermarks should be on the paper used by certain artists are crucial in helping to authenticate a print.’

Modern British art

‘Condition can be key when it comes to appraising a painting,’ states Pippa Jacomb, director of the Modern British and Irish Art department at Christie’s. ‘If the painting is on canvas, I check to see if it has been lined — meaning that a secondary canvas has been attached to the original to provide additional support and stability. If it has, I want to know why.’

In Jacomb’s specialist field of 20th-century British pictures, lining is fairly unusual because the paintings are, relatively speaking, quite new. ‘But if they are lined it could be to support restored paint and repaired cracks,’ she says, ‘or to strengthen the canvas if it’s been torn.’ Although many canvas linings are very sensitively applied, older linings can have the effect of flattening a picture’s painted surface.

Jacomb says the next step is to check the work’s condition under ultra-violet light. ‘More recently applied pigments on the canvas will fluoresce, glowing purple, highlighting areas of restoration and retouching not visible to the naked eye or under natural light,’ she explains.

Increasingly, collectors are sensitive to condition. ‘They want to know as much as possible about a painting’s history and any work undertaken on it,’ the specialist says. ‘This also can help inform any conservation that might be needed in the future.’

‘When we appraised L.S. Lowry’s A Northern Race Meeting  in 2018, we couldn’t believe what beautiful condition it was in, especially considering it’s over 60 years old and an impressive 30 x 40 inches in size,’ recalls the specialist. ‘The original, untouched condition is just what collectors look for and undoubtedly steered the price at auction to £5,296,250.’

Post-war and contemporary art

‘When inspecting paintings I am curious to see the back of the work, as there could be old labels, stamps, stencils and notes on the reverse of the canvas and its stretcher,’ says Leonie Grainger, Senior Director of Post-War and Contemporary Art at Christie’s. ‘These give important clues regarding the work’s provenance and exhibition history.’

Often these labels stuck to the back come from galleries which have sold the work, and sometimes private collectors have their own stamps, she says. These can be cross-checked to trace a painting’s provenance and help prove authenticity.

‘With a bit of luck,’ adds Grainger, ‘there will be historic labels from museums and exhibitions that displayed the work, which add to its exhibition history and associated literature. Furthermore, there might be stamps and numbers from an artist’s authentication board, which are reassuring for collectors and can increase the desirability of a work.’

The reverse of paintings by the American-German artist Josef Albers can be among the most interesting, says Grainger. As well labels from museums and galleries, they often contain Albers’ precise notes about the colour pigments and varnish he used for the painting. ‘Should the work ever need to be restored,’ notes the specialist, ‘this could prove more than helpful.’