ORAN Mor, on Glasgow’s Byres Road, seems as good a place as any in which to talk about the artistry of Alasdair Gray.

After all, his magnificent mural in the auditorium – “the Sistine Chapel ceiling for Scotland’s working class”, as Gray himself once said – is one of Oran Mor’s most distinguishing features. Another of his large-scale murals is but a short stroll away down Byres Road, at Hillhead subway station. Further works of his can be glimpsed at the Ubiquitous Chip, in Ashton Lane. As a New Yorker article put it in August 2015: “Gray’s presence in Glasgow is persistent and mercurial: you never quite know where he’ll crop up next.”

The man himself, of course, is now 82, and he has been recovering from injuries sustained in a fall at his home in June 2015. A message on his website says he is “much better than he was and back working on all the things he needs to get done. His mobility remains affected, but he has lots of friends who love him dearly so, he is well looked after”.

Rodge Glass, sitting one recent lunchtime in Oran Mor’s Whisky Bar, knows Gray exceptionally well. He was once Gray’s secretary (“that was my writer’s education, essentially”), and he went on to write Alasdair Gray: A Secretary’s Biography, which won a Somerset Maugham award in 2009. A novelist and academic (he’s a Reader in literary fiction at Edge Hill University in Ormskirk) and associate editorial director at Glasgow-based Freight Books, Glass is now at work on his next project, which takes as its subject Gray’s prodigious array of artworks.

His co-author on The Essential Art Of Alasdair Gray is none other than Sorcha Dallas, Gray’s art agent. The book will span Gray’s murals, portraits, landscapes and installations. Some impressive names have already submitted their written contributions, but Glass and Dallas are keen for ordinary people to nominate their own favourites. Ten of those responses will be included in the book when it is published in October. All of them will be featured on a dedicated website.

“At the time I was writing the biography,” Glass says, “there were a broad range of people breaking down the door to tell you what they thought of Alasdair’s literature, but it was really very tough to get anybody to comment on the art. And usually, whenever anyone commented on it, it was in the context of the books: the illustrations in Lanark, say, or Poor Things, or Unlikely Stories, Mostly.

“Trying to get anyone from the art world to say anything – someone who wasn’t Alasdair’s pal, or who wasn’t already positively inclined towards him – was incredibly tough. So I was conscious of a gap there and was desperate to find somebody to put it into context for me, to say, where did his art come from? What was it influenced by? Has it made a contribution and, if so, what?”

Why was it so hard to elicit that sort of comment from the art world at that time? Glass says that back then, Gray’s art was “commercially valueless. Paintings were lost; sketches were done for free in the pub and then lost”. Furthermore, “at that time, he was a footnote in a footnote in a footnote even in Scottish art literature, never mind British or European. But that has radically changed in the decade since. There’s been a huge mushrooming [of interest in Gray’s art] since that time. When I was writing the biography, Alasdair was writing his book, A Life In Pictures, which took him 15 or 20 years … He said part of his reason for doing it was because nobody else had written about his art.” Glass recalls a double-page spread in a “tiny, indie Scottish art book”, on Gray’s 1964 painting, Cowcaddens Streetscape In The Fifties; he “was only really included in it because he was a writer”.

Gray’s work is now being bought by major collections, locally, nationally and internationally. An estimated 35,000 people flocked to see various Gray exhibitions across Glasgow in 2014, including 20,000 for Alasdair Gray: From The Personal To The Universal, a major retrospective exhibition at Kelvingrove in 2014-15. A generation of younger artists now cites him as a key influence too. “How things have changed,” observes Glass in a separate email. “Oh to be fashionable at the end of your life!”

Glass and Dallas's book is partly an attempt to make sense of the burgeoning interest in Gray's work over the past decade. "We’re also bringing it out now because a lot of people are very keen to critique Alasdair’s art and to celebrate it," says Glass. "And at this time in his life, I just think it’s so weird – typically Alasdair, somehow – that the reception to the art has something like a 50- or 60-year lag on the literature, but it’s catching up fast.”

Born in Riddrie in December 1934, Gray was a voracious reader as a child, alighting on such writers as Dickens and Stevenson. He attended Glasgow School of Art between 1952 and 1957 and went on to write a considerable number of plays for television, radio, the stage and schools. From 1952 onwards he painted a series of murals on a wide range of subjects, the earliest being one called Horrors Of War, for the Hillhead-based Scottish-USSR Friendship Society. In 1962-63 he was a scene painter at the city’s Pavilion and Citizens theatres.

It wasn’t until 1981 that he published his first novel, the award-winning Lanark. The Guardian would later say of it that it “changed the landscape of Scottish fiction, opening up the imaginative territory inhabited today by writers such as AL Kennedy, James Kelman and Irvine Welsh”.

Subsequently, Gray, to quote from his CV on his website, has lived “almost wholly by writing, designing and illustrating books, mainly his own”. Later works included Unlikely Stories, Mostly (1983); 1982, Janine (1984), a novella, The Fall Of Kelvin Walker (1985), Poor Things (1992), more short stories, Ten Tales Tall & True (1993) and Old Men In Love (2007).

A staunch supporter of the idea of an independent Scotland, Gray wrote, in 1992, Why Scots Should Rule Scotland; in 2014, on the eve of the referendum, he brought out Independence: An Argument For Home Rule, the jacket copy of which asserted that "a truly independent Scotland will only ever exist when people in every home, school, croft, farm, workshop, factory, island, glen, town and city feel that they too are at the centre of the world".

Gray’s second wife, Morag McAlpine, died in May 2014, aged 64, after a short illness; Inge Sorensen, his first wife, and the mother of his son Andrew, died in 2000.

Part of the purpose of Glass and Dallas's forthcoming book will be to redress something else that Glass has noted: that, for all Gray’s ubiquity in his native Scotland, he becomes strangely absent once you cross the Border. The co-authors are thus searching for an international, multicultural gallery of names who are willing to speak in admiring terms about Gray’s art, and to spread the word further still.

The roll-call of notables who have so far agreed to contribute to the book is undeniably impressive. So far, there are between 55 and 60 names. “[Artist] Douglas Gordon is doing a chapter,” says Glass, consulting his open laptop on the table. “Alex Kapranos, from Franz Ferdinand.” Jackie Kay, the Makar, will write about Oran Mor. Lots of others have committed themselves to the cause. Novelist Janice Galloway is writing about a sketch Gray did of her son.

Novelist Will Self, as a note in the Alasdair Gray section on Sorcha Dallas’s website reminds us, is an admirer of Gray’s illustrations: “all firm, flowing pen-and-ink lines, precise adumbration, colour – if at all – in smooth, monochrome blocks”. The note also recalls an observation once made by Dr Elspeth King, former curator of the People’s Palace in Glasgow, about how Gray was a master of line in both writing and art, and each publication of his was as much a work of art as it was a work of literature.

“We’re looking at people who have bought Alasdair into major galleries at home and abroad,” continues Glass. “The book will have around 10 people from the world of literature. There will be lots of fellow-artists represented, too, and collaborators.

“A large part of what interests me about Alasdair’s art is that it is so democratising. Take the mural [at Oran Mor]. You’ve got the Garden of Eden juxtaposed with contemporary Glasgow, and some of the most famous characters in history right next to people who work in the bar here. It’s that juxtaposition that I think is interesting.

“But Alasdair has always had to work with lots of collaborators, so [in the book] there will be about 10 people who worked with him on various major works. There’s a former assistant called Nichol Wheatley, an extraordinarily important Gray collaborator on the Hillhead and Oran Mor murals. We’ll have contributors from media and politics: hopefully we’ll have a couple of really high-profile people from these. We’ll have family and friends, and people who have appeared in the works and murals. Academics, too”.

The first Alasdair Gray international conference was held at the University of Brest, in France, in November 2012 [Glass and Dallas both addressed it], and there are now specialists in his work all over Europe and as far away as Mexico.

One personal contribution is being supplied by the novelist Bernard MacLaverty. Glass smiles as he says that the front cover of Poor Things [winner of both the Whitbread Novel Award and Guardian Fiction Prize], features a “grotesque portrait” of MacLaverty, author of works such as Lamb, Cal and Grace Notes. When Gray was writing the book, he and MacLaverty would play chess every week as Gray did all the voices from the developing story. “Bernard was egging him on, telling him it needed to get bigger and bigger and bigger. It came out in no time, and Alastair asked whether, in return for Bernard’s help, he could do his portrait for the cover. It’s a credit to Bernard’s good humour that he didn’t take offence at the illustration. Not everyone would be so relaxed about it."

The democratisation inherent in Gray’s work is reflected in the co-authors’ insistence on getting contributions from unsung and unnoticed admirers of Gray’s art. Ordinary people who adore, say, his book illustrations, or one of the artworks that were on show at Kelvingrove, or one of his murals in the West End.

“For the next few months we’re putting the call out for anybody who loves Alasdair’s art to tell us, in 250 words, which is their favourite image and why,” says Glass. “We will put together a website, a public archive, for all of them, and we will pick 10 to go into the book itself. We hope this will be a meaningful nod to Alasdair’s own view of the world – that the great and the good are all very well, but it’s important to have people represented who are not artists.

“We want people to tell us what speaks most to them about their chosen piece. It could be something technical, it could be something personal; it might remind them of a particular time in their life. It could be a portrait of someone they know.”

How is Alasdair doing at the moment? “He’s doing okay,” says Glass. “He was very ill for a long time but he is certainly working. He’s doing it slower; he’s wheelchair-bound, but he has support coming in every day. It’s a huge, huge challenge but he’s taking it exactly as you would expect Alasdair to do. He’s spending his time writing a Scots version of Dante’s Inferno: what else would he be doing to pass the time? But he’s the first to admit that he’s not as strong as he used to be.”

The forthcoming book is also partly about the time of life that Gray now finds himself at. Glass observes that he was asked to update the biography, but he decided it wasn’t for him. “Things have changed. I thought this is a more honest way of doing things. I thought it was an opportunity to do one more interview, one more portrait. In the new book I’ll do an introduction that bridges then and now. Because although the early 2000s were fascinating to me, because that’s what I close by to see [of Gray], the last decade has been far more interesting, both in terms of his life, and critically, too. And I think that needs acknowledging.”

• To nominate your favourite of all Alasdair Gray’s artworks, send a 250-word email to mail@theessentialartofalasdairgray.com You can also contribute via Twitter at @essentiallygray. The deadline for all contributions is the end of May.