Made an Honorary Royal Academician just a few months before he died, in 1993, it’s taken till now for a posthumous Royal Academy survey to finally bring one of the absolute greats of American postwar painting to a UK audience. Of course, for those with long memories, there was the Whitechapel Gallery exhibition of 1991, but though it provided the impetus for the belated honour, it seemed to do little to bring the paintings of Richard Diebenkorn into the public realm.

The unveiling of the Fourth Plinth has, since his election to office, been an opportunity for Mayor Boris Johnson to work the press pen with a comic turn. So, the commission, sponsored by the mayoral office, gets a media-chummy spokesperson whose art critiques add a note of gaiety to proceedings, even if they’re self-evidently at odds with what the artist had in mind. See them as an ongoing election campaign. 

Here is an exhibition that tells us how something we now take totally for granted actually came about: how our love affair with the Impressionists was masterminded by an art dealer, Paul Durand-Ruel (1831-1922). He was a prime mover in inventing the way art is dealt with by commercial galleries and even museums, and is credited as the inventor of the modern art market.

The sight of two old women fighting in the street would probably meet with roughly the same response from passers-by whether it happened today or 200 years ago – a queasy mixture of dismay, embarrassment and amusement. To get close to Goya’s drawing of two ancient crones locked in a wrestlers’ embrace, their toothless faces both grimly determined, is to experience those uneasy sensations just as he surely did.

Recent attitudes to Victorian Britain have changed radically. The popular view used to be of a period filled with a kind of smug imperial confidence, underwritten by the increasing wealth of the industrial age. This ingrained assumption was perhaps epitomised by Lytton Strachey’s 1918 Eminent Victorians, which saw the eminences as bungling hypocrites. And although secret lives might have been as wild as may be, one characteristic myth was that even piano legs had to be obscured with frilly covers for decency. 

So, Picasso’s last words turned out not to be, “Drink to me. Drink to my health. You know I can’t drink anymore” – yes, those famous last words that inspired a Paul McCartney dirge – but were, according to this TV biography looking at Picasso’s women and how each significant relationship informed the direction of his work, “Get me some pencils”. A more prosaic request, certainly, but he died in bed, aged 93, his pencils delivered and drawing to the last. It was a good and fitting end.

Captured in monochromes ranging from the most delicate honeyed golds to robust gradations of aubergine and deep brown, the earliest photographs still provoke a shiver of surprise and excitement. Even now, their very existence seems miraculous, and the blur of a face, or the lost swish of a horse’s tail signifies the photographer’s pitched battle with time, never quite managing to make it stop altogether.

The Whitworth Art Gallery was showered with meteors in a spectacle devised by the artist Cornelia Parker on its reopening weekend – appropriately Valentine’s Day. The £15m project (architects MUMA) has doubled the exhibition spaces, reclaimed the Victorian Grand Hall from offices, added state-of-the-art on-site storage and more space for conservators.  

Sotto Voce is a collection of white paintings, sculptures and reliefs made by European, British and North and South American artists from the 1930s to 1970s. An accompanying book explains why this non-colour has appealed to so many artists in so many countries over such a long period of time.

The title has it about right: no matter what it is they are busily acquiring, collectors seem to be an obsessive bunch, and their obsessions can achieve quite magnificent proportions. The stereotyped image of the collector as a socially challenged monomaniac doesn’t really fit with the popular understanding of the artistic temperament, though.