Visual Arts/Aidan Dunne Reviewed: Charles Tyrrell, Fenton Gallery, Cork ends today (021-4315294) Jacqueline Stanley, Isles and Ocean, Vangard Gallery, Cork until August 2nd (021-4278718)

You can be sure that the work in a Charles Tyrrell exhibition will be clearly stated, consistent and forcefully argued. There is a stubborn, hard-won quality to his paintings, an air of rigour and determination. This isn't incidental. To get onto the wall of the gallery, a painting by Tyrrell has to survive a gruelling course of self-criticism on the part of the artist, for which we, the eventual viewers, and in some cases collectors, should be quietly grateful. We should be grateful because that level of sustained, critical concentration is, alas, all too rare.

It would be fair to describe Tyrrell's work as abstract but it is not dogmatically so. There are, for example, aspects of the colours, tones and textures in much of what he does, work that suggest associations with landscape. But it's more that certain aspects of his environment have seeped into his painting than that he has made any conscious bid to deal pictorially with his immediate surroundings. While he makes paintings and drawings in coherent groups or series, there is a dynamism built into his working process which means he has never settled into a fixed, predictable pictorial formula. Each new series carries the argument onwards.

There are stylistic consistences, however. He favours a square format and his compositions are based on grid patterns.

The given symmetry of the grid is variously endorsed and disrupted from work to work. Recurrently, there is a play on mirroring that doesn't quite match. What happens is that a fault line, or a zone of slippage, bisects the composition, knocking out the potential symmetry. Previously, he has deployed a number of centrally positioned forms, irregular in outline, and subjected them to this discontinuity.

In his new work, he has, with one partial exception (in which a kind of scrambled version of such forms appear), dispensed with them. In fact, the language used in these paintings is exceptionally, perhaps deceptively, simplified and spare. There is just the underlying grid and a few surface subdivisions, horizontal and vertical. But that zone of slippage is absolutely central, literally and figuratively. Each square is quartered by vertical and horizontal divisions, but in terms of what is going on in the paintings, priority is given to the vertical division. Narrow bands form borders that reinforce the constituent squares.

While the surfaces are quite slick and polished, there is clear evidence that every painting is densely worked, subject to an incremental process of layering, progressively built up and scraped back. Residual traces of layers over-painted or scraped away show through. Shades of grey and fairly dense blacks dominate, although there is a great deal of colour built into the paintings and in one case, C7.03, a startling double-blast of vivid red.

Because the history of their making is, to a significant extent, apparent in the finished paintings, looking at them we are instinctively aware of the various possibilities of covering and uncovering that the artist has gone through, within a set of self-imposed rules. There is a rightness to each, but also an essential tension. Yet the really striking thing about them is the way in which everything that goes on, everything that leads our eyes and minds along, is a kind of diversion.

What is happening is that we are being moved around each particular painting but consistently deflected from that central zone. There are two ways of looking at what is going on in that zone. One is that, in terms of the logic of the paintings, nothing can be there. That's the rule. The other is that everything about the paintings is a way of avoiding being there.

Either way, it is clear that the zone is a space that cannot be occupied. It's both part of and apart from the paintings in that it's crucial to them, energising the surfaces to either side, and simultaneously outside of or beyond them. It's extraordinary how well its mere existence is disguised in many of the paintings, so efficiently do they exercise our eyes and our minds.

Yet the tension of the compositions derives in no small measure from this implicit condition of their making.

You may think that these ideas sound unlikely, but if you look at the paintings attentively you may be prompted to agree that they do describe how they work. And, furthermore, they are entirely typical of Tyrrell's exceptional management of the dynamics of space and surface. This series of paintings, with their pared-down vocabulary, their sustained concentration and their determination to push the possibilities to the limits, represent Tyrrell at his best. That is to say, as a painter of exceptional quality in a national, or indeed any, context.

Although there is a significant number of oil paintings in Jacqueline Stanley's Isles and Ocean at the Vangard Gallery, her flair as a draughtswoman still dominates. She uses oil paint very well, though with a distinctive personal spin, cutting into areas of colour to build up rhythmic, linear patterns, for example. The construction of fluent linear armatures is her characteristic way of sorting out space and movement in a composition, and she is extremely adept at it by now.

There are three landscape sources for her work here: Skye, Ballinskelligs and what is effectively her home ground, west Cork around Roaring Water Bay. A series of dense, briskly worked pastel drawings of windows at each location lead us out into sweeping, expansive spaces. Her expertly organised compositions are atmospherically very good and invariably capture the dynamism of weather moving across and animating the landscape.