Emerging from the shadows of Siar 50 is a hidden collection of contemporary Irish art spanning 50 years, writes Aidan Dunne

Siar 50 at Imma was originally conceived in 2000 as a tribute to the late Gordon Lambert who died in January 2005. One of Ireland's foremost art collectors for many decades, Lambert was also a stalwart of the Contemporary Irish Art Society, the CIAS.

A member for 40 years, he also served as the organisation's president and patron for long periods. Modelled on Britain's Contemporary Art Society, which has been active since about 1910, the CIAS raises money from its members for the acquisition of art works for public collections. It was initiated, on a relatively informal basis, in 1962.

At the time, opportunities for Irish artists were few. The country's economy was still in the doldrums. The audience for contemporary art was small and collectors were rare. Official support was negligible compared to today. The acquisitions budgets of public institutions were generally inadequate. As Campbell Bruce relates in the catalogue of Siar 50 (which takes its name from the Irish word for back or looking back), the renowned Dublin art dealer Leo Smith, of the Dawson Gallery, in conversation with Cecil King, Patrick Scott and Stanley Mosse, came up with the idea of an Irish version of the Contemporary Art Society.

An initial group, chaired by the indefatigable Basil Goulding, chipped in £10 each and bought a painting to give to Dublin's Hugh Lane Gallery. The membership of the society grew, ensuring a steady stream of donations to, initially, the Hugh Lane. These donated works were extremely important for the gallery, for Irish art in general and indeed for all of us, the wider public.

Considered in the context of the overall collection, the CIAS contributions form the core of the Hugh Lane's holdings of Irish art at mid-20th century. Smith had identified a cultural problem and had managed to do something about it. The society's immediate aim has always been to support Irish artists, particularly younger artists, and direct patronage was and is the best way to do this. It means that the nature of the acquisitions has always moved with the times.

As the society grew (its membership, now well over 200, had reached 99 by 1973) the scope of its activities developed. A staggering 40 public institutions have been the beneficiaries of donated works. They include Imma itself and practically any gallery you can think of.

Lambert had an eye to the public good throughout his years with the society. Dismayed by the break-up of Basil Goulding's collection after his death, Lambert formed a trust to ensure that the same fate did not befall his own. He was a tireless advocate of the need for a national museum of modern art and, indeed, it was his advocacy, along with that of others, that led to the establishment of Imma. His collection is a cornerstone of Imma and, more, the trust he established continues to support additional purchases for the museum.

There are strong links between the Hugh Lane and the CIAS, and originally the idea was that this exhibition be held there. In the meantime, however, plans for an extension to the Hugh Lane swung into high gear and the gallery is more or less out of action until March. Given Lambert's significant role in Imma, it was an obvious alternative. The work acquired and donated by the CIAS makes up a kind of shadow collection of contemporary Irish art, one dispersed invisibly throughout the country.

Previously, in 1993, Bruce was involved in curating an exhibition of work from the collections of CIAS members at Imma. It was, he recalls, an eye-opener.

On reflection, it stands to reason that many of those involved in the society would be discerning and enthusiastic collectors in their own right.

Hence the idea for Siar 50, which draws on both works acquired for public collections by the CIAS and works from members' own collections. What emerges from the shadows, so to speak, is that hidden collection of contemporary Irish art, spanning the past 50 years or so.

It is immediately noticeable that the exhibition includes many pieces that could reasonably be described as classics or classics-to-be, key pieces by artists who are important figures in Irish art. Among such works would be Patrick Collins's Hy Brazil, painted in 1963 and given by the society to the Hugh Lane Gallery. An evocation of the mythical island in muted, lyrical greys, it represents Collins at his best, somehow combining a hard, unsentimental view of things with unapologetic romanticism. Hy Brazil, as a sort of distillation of Celtic Irishness, symbolises Collins's feelings about his own identity, while a hard, abrasive quality reflects his ambivalent view of workaday Ireland.

That first crop of purchases was particularly inspired, and the Hugh Lane benefited greatly. In fact, the very first acquisition was Patrick Scott's Large Solar Device, one of a series of audaciously spare paintings that established his mature style. His immediate inspiration was fission rather than fusion. He had in mind the nuclear devices undergoing test explosions at the time but, for Scott as for Turner, the sun's the thing.

Another brilliant choice was Barrie Cooke's Nude, in which the boldly indicated figure, her legs parted, seems to merge with a dark, deep watery current that envelopes her. A shimmering, mysterious image, it encapsulates Cooke's vision of organisms as nurtured, moulded and shaped by flowing processes within their environments.

Sean McSweeney's Evening Shoreline is a remarkable painting. For one thing, it seems to be darker than it actually is. McSweeney has established a set of tonal contrasts that conveys both the sense of infinite night-time darkness and the persistent luminescence of the sea. It's crisply made and authoritative, and a prime example of a wonderful body of Sligo shoreline pictures that play a central role in any account of Irish landscape painting.

Mary Lohan's Windswept Ravines, Co Donegal and Gwen O'Dowd's Cladach 21 are also terrific, well nigh flawless examples of the work of two leading painters whose work is rooted in landscape. Both embody the rugged, worn, weather-beaten quality of the western seaboard terrain in slightly different ways.

Cecily Brennan's cast stainless steel sculpture, Bandaged Heart, is a tremendously effective work, a complex amalgam of violence, hurt and tenderness very simply expressed. It is an unforgettable piece that consolidates a sea change in her approach, with her move to a traumatic vocabulary of damaged bodies.

Other artists represented by superlative examples are the sculptors Michael Warren and Gerda Fromel, whose exceptionally elegant sense of form comes through in her Marble Head. Edward McGuire's portrait of Patrick Collins, Martin Gale's evocation of rural life, Charles Tyrrell's rigorous abstract, Eithne Jordan's doubled head, Janet Mullarney's fluent, subtle variation on the theme of mother and child, Kathy Prendergast's variation on the theme of the vessel and Nick Miller's slice of frenetically detailed landscape are all equally outstanding. This is not to say that there are not many more good works by good artists in the show, but those mentioned have the quality of being more than the sum of their parts, somehow summing up what an artist had or has done, and perhaps will do. It is in all a brilliant calling card for the CIAS.

Siar 50: 50 Years of Irish Art from the Collections of the Contemporary Irish Art Society is at the Irish Museum of Modern Art, Kilmainham until Feb 19