In a dark cluttered studio in central Florence, restorer Rossella Lari is working on a little-known jewel of the Renaissance. It’s vast: a seven metre by five metre depiction of the Last Supper, with figures that are almost lifesize, that was painted in the 1560s.

As she works, Lari says she thinks often of the person who painted it. “You get to know an artist when you restore their painting,” she says. “You learn about them from the way they use the paint, from their brushstrokes, from their attention to detail.” This artist, she says, was strong, confident and determined. She had to be, because she was also female, the earliest significant female Renaissance artist.

Her name was Plautilla Nelli (1524‑1588), and the painting Lari is working on is her masterpiece. When it’s finished, in 2019, it will go on show at the Santa Maria Novella Museum in Florence, the first time it will have been publicly exhibited in 450 years. “That is a very significant moment, not only for Nelli but for all the forgotten women artists of the Renaissance, as well as for artists today who don’t realise how rich a contribution women made to that era,” says Linda Falcone of Advancing Women Artists (AWA), an organisation championing forgotten works.

Facebook Twitter Pinterest Unfairly neglected … Rossella Lari restores The Last Supper by Plautilla Nelli.

Ask most people to name a female artist, and chances are they will come up with a contemporary figure: Tracey Emin, Rachel Whiteread or Paula Rego. Or they’ll name a 20th-century artist such as Frida Kahlo, or Georgia O’Keeffe. What they won’t do, though, is name one of the 16th- or 17th-century women who painted during and in the years following the Renaissance. Nelli is one of many female artists – including Artemisia Gentileschi, one of the most accomplished followers of Caravaggio, and Marietta Robusti who learned from her father Tintoretto – that history has unfairly neglected.

Now, though – nearly half a millennium on – that is beginning to change. AWA, which was established in 2009 by US philanthropist Jane Fortune, is committed to rediscovering all the works by women that lie forgotten in the museum attics and churches of Florence: at least 2,000 so far. When a painting is found, crowdfunding and special appeals pay for its restoration: $67,000 (£50,000) was raised in six weeks to pay for the first stage of the restoration of Nelli’s Last Supper, and another $145,000 is now being sought. “People want to see these works restored,” says Falcone. “They’re a missing piece of history, and they’re also very beautiful and important paintings.”

Look what's on the table! Plenty of food – lambs, beans and salad – and plenty of wine

To help me understand the significance of the Nelli work, Falcone takes me first to see another Last Supper, painted by Andrea del Sarto, who was described by Giorgio Vasari as being “without errors”. The painting, a fresco on the refectory wall of the convent of San Salvi that dates from 1526-7, is effortlessly naturalistic, beautifully balanced and vibrantly coloured. “It’s a wonderful work,” says Falcone. “One of my absolute favourites. But look at the tablecloth – it’s so scruffy! And this is a meal, but where’s the food? This table is empty, apart from some bread … ”

Nelli’s Last Supper, which takes up an entire wall of the crowded studio in which Lari works, shows the same scene with some significant differences. “The tablecloth is neat and has been folded, for one thing,” says Falcone. “But look at what’s on the table! There’s plenty of food, including lamb and beans and salad: food for everyone, and plenty of wine.” There’s a very earthy, everyday feel to the composition; as well as providing for the figures at her table, Nelli has also taken great pains over the apostles’ physique. “She was very interested in anatomy, and you can see that in the painting,” says Lari. “Look at the hands; she’s put so much detail into them.”

Facebook Twitter Pinterest A figure from The Last Supper shows Nelli’s attention to anatomical detail. Photograph: Francesco Cacchiani

But perhaps the biggest and most significant difference of all is in the representation of the Christ figure. In Del Sarto’s work he sits alone majestically; he seems to be talking, perhaps teaching his followers. In the Nelli work, he is almost maternal. “St John is leaning against him, and Christ is holding him,” says Falcone. “You get a quite different sense of the Jesus in Nelli’s painting.”

Nelli was a nun at a time when convent life was often more liberal than life in the outside world. From her convent she ran an art school for other women, a crucial enterprise when women were unable to train as artists (nor could they join the all-important professional guilds). Women supported each other: some of Nelli’s commissions came from the prioress of her Dominican convent. One shows St Dominic receiving the rosary from the Virgin, the other is St Catherine receiving the stigmata. Both were rescued by Falcone and her colleagues from the attic of the Pitti Palace. “They were in such a bad way that at first the museum authorities didn’t want to try restoring them,” she says. Today, they hang on the wall of the San Salvi Museum.

Women were thought to be more detail-oriented and detail on jewellery and clothing was important as it conveyed status

One oddity of the story of the Renaissance women is that they seem to have been more valued in their own time than they were subsequently. According to figures from the feminist art activist collective Guerrilla Girls, female visual artists earn 81 cents for every dollar made by a male artist. But in the Renaissance and baroque eras, says Falcone, painters such as Nelli and Gentileschi were better paid than many men for their work: at one point Gentileschi was earning five times more than her male counterparts. As portraitists they were particularly valued, because portraits were used to clinch marriage deals.

“Women were thought to be more detail-orientated, and detail on jewellery and clothing was important because it conveyed status,” says Falcone. “They were also considered more capable of capturing psychology.”

Nelli clearly seems to have regarded herself as a serious player in the art world; if she hadn’t, she would not have tackled the Last Supper, the quintessential Renaissance subject. Only those artists who considered themselves greats even attempted it; it took large amounts of strength, time and resources. “She would have been working with assistants, and she’d have had to use scaffolding to cover a canvas this large,” says Lari. “Physically, undertaking a work like this was a big deal.”

Before it was removed for restoration, Nelli’s Last Supper was on the wall of the Santa Maria Novella monastery in whose refurbished museum it will soon hang. Many of the other works being rescued by AWA are much harder to locate; but the task is being made a little easier by a historical quirk of fate, as Falcone explains. “In 1966, Florence suffered terrible floods: at least 14,000 works of art were destroyed in the deluge, and many more were damaged. And because of that, restoration became a growth industry, and many of the people who trained to do that work were women. And then those women started to think about the paintings they were working on and started to ask: where are all the women? And then they realised there were some women, but their work had been hidden: forgotten in attics, or wrongly attributed to men.”

Facebook Twitter Pinterest Bit by bit … the restoration of Nelli’s Last Supper Photograph: Francesco Cacchiani

Elizabeth Wicks, an American who has lived in Florence for many years, is one such restorer. “These paintings are hidden in plain sight, all over the city, and it’s so exciting to be part of the operation to bring them back to the fore,” she says. She takes me into the sacristy of Santa Maria Maddalena de’Pazzi where there is a painting of the Virgin presenting the Christ child to the church’s eponymous Florentine noblewoman and saint. It’s a copy of an altarpiece in the same church by Luca Giordano, painted 80 years previously. The creator of the sacristy work was the 18th-century painter Violante Siries Cerroti, the daughter of a Medici court engraver and a practitioner talented enough to have a portrait in the Vasari Corridor, where works by the famous masters are exhibited.

The sacristy painting, says Wicks, “had been very badly damaged in the 1966 flood, and when I first saw it I was horrified. If much more time had gone by, it would have been irreparable.” Siries, she says, was the first female artist allowed into the Uffizi to make copies of the works there. Like Lari, Wicks feels a great affinity with her artist: “Siries was about my age when she did this work, and she was a working mother who needed to make a living. I can identify with that. It was physically challenging work, and she was meticulous in the details of the dress and the lace. There is also a wonderful light to the painting.”

The great flood of Florence, 50 years on Read more

Nelli, whose work was shown in an exhibition at the Uffizi for the first time in the spring of 2017, was clearly aware of the danger that history would sideline her. Though the tradition of the day was not to sign a masterwork such as her Last Supper, she defied convention and made her mark: Lari shows me her signature, top left. In his appraisal of her, Vasari wrote that she could have achieved wonderful things, if only she had been given the opportunity to study as men were. But for her champions in Florence today, Nelli did achieve wonderful things; and soon, we will all be able to see more of them.

• For more information about AWA see advancingwomenartists.org.