Elizabeth Blackadder has been a respected, but curiously peripheral, presence on the British art scene for several decades now. She is respected for her exceptional skill as a painter, for her brilliance as a watercolourist and graphic artist, and for her work as a teacher.

Her peripheral status is attributable to many factors. First of all, she opted to live not in London but in her home country, Scotland. Then, though she is not hidebound by convention, from the first she attracted considerable official approval and her work is always sufficiently decorative in its concerns to align it with the Academy. So although it is fresh, inventive and not at all as conventional as it might seem, it has usually been slotted into the pigeon-hole labelled "conservative".

Furthermore, her nominal subject matter - landscape, still life, flowers, and even cats, for heaven's sake - seems essentially comfortable, domestic and unchallenging. In other words, it is the antithesis of issue-driven art. And Blackadder has always tried to do things as well as she possibly can. She has continually honed her technical skills and her intuitive feeling for a small range of traditional media and materials, which of course means an unfashionable emphasis on craft, rather than concept.

If this seems like a needlessly graceless way to introduce an artist whose prints make up the centrepiece exhibition of this year's Earagail Arts Festival, it is only a preamble to stating that her work, when you encounter it, is simply so good that it easily transcends any implied limitations or reservations. The main, one-person show, at the Letterkenny Arts Centre, features more than half the prints she has made at the Glasgow Print Studio. Many others are included in the subsidiary shows, which feature work by others artists as well.

Blackadder's involvement with the studio, which dates from about 1985, has been an extraordinary success, both critically and commercially, and because it has opened up a whole new area of exploration for her. Blackadder and print, particularly etching, were made for each other. Her drawings - and, to some extent, her watercolours - are distinguished by the incredible quality of her line. Something produced, that is, by a combination of inherent ability, practice and refinement, and the sheer nervous energy bound up in the moment of making a drawing. Her line can be sinuous and seemingly casual, and it can be absolutely taut and incisive, but it is always fluently, crisply precise. Of course, she uses light and shade, and she uses colour widely and well, but print brought out the strong linear quality of her work.

Elizabeth Violet Blackadder was born in Falkirk, Stirlingshire in 1931. She grew up in a fine sandstone house next to the family engineering works. Her brother describes her as resembling their father in character: quiet, thoughtful, gentle but with an underlying strength of mind. She is still famously reticent about commenting on her work, and statements are few and far between: "The work is all based on some point of reference," she wrote, guardedly, in 1979, "although it may move away greatly from the starting-off point before it is finished." It is interesting that, latterly, her fidelity to external appearances has actually increased.

Given the importance of flowers as a subject later on, it's worth noting that as a young girl she built up a fine collection of pressed local flowers, all labelled with their botanical names. Visits to the Glasgow Art Gallery brought her into contact with the work of the Scottish Colourists, a loose-knit group of artists influenced by French painting. She studied art at Edinburgh College of Art, under William Gillies, one of the leading lights of the relatively progressive Edinburgh School which emerged in the 1930s.

Blackadder married a fellow-student, John Houston, and the two are widely held to exemplify a mutually supportive and work-oriented relationship. The pair have consistently travelled, and travel has informed the evolution of her personal style, sometimes fairly obviously as, for example, in the case of their trip to Japan - though it has to be said that an Eastern influence was already evident in her work.

They have also visited France frequently since the early 1960s. Equally, India has been an important presence, not least in the form of the language of its painting. Blackadder was greatly impressed by the exhibition of Indian painting organised by the dealer Kasmin and painter Howard Hodgkin in London in 1968. An inveterate collector of objects, to make her still lifes she draws on an extensive collection, encompassing such things as Indian boxes and brightly coloured toys, carved wooden animals, paper kites, fans, bowls, stones, pieces of fabric, ribbon, coloured paper and, of course, flowers and all manner of exotic fruits.

Her characteristic approach to still life is to arrange a miscellany of objects on a plain table-top and, instead of offering a perspective view of the ensemble, depicting them flatly and separately distributed against the neutral ground. The result is like an inventory of objects, patterns and colours that you explore at will.

From 1963 she and Houston had a garden - at first a small garden, then, after another move in 1975, a much bigger and reputedly magnificent garden in Fountainhall Road in Edinburgh. By 1966 she had started drawing flowers and, as time went by, they became a significant strand of subject matter. Blackadder's involvement in botanical illustration began in 1979, when she collaborated with Dr Brinsley Burbidge of the Royal Botanic Gardens in Edinburgh in organising an exhibition of botanical illustrations, The Plant. The same year she made what might be regarded as her first botanical work per se, a study of an amaryllis and a crown imperial.

Within the frame of fine art, botanical illustration is one of those areas that have been consistently downgraded, because it is perceived as being functional, mechanical and, arguably, because it was often done by women. While plants had been a subject for Blackadder for many years, she approached them in a way curiously in between naturalistic representation and botanical observation. Together with a meticulous account of a flowering hibiscus, for example, she would include images of the cats who happened to be lying on the grass. Inevitably, some observers feel that her work is too informal to stand as being strictly botanical, while others argue that it's too botanically inclined to be art. Of course it is both. The liveliness of her line brilliantly conveys a sense of the living plant in a way that a more pedantic rendering never could, without any sacrifice of accuracy or clarity. Relish the chance to see so many of the prints in one venue.

Elizabeth Blackadder - Printmaker is at the Letterkenny Arts Centre until August 25th. 20000, Part 1 is at An Grianan Theatre, and Part 2 is at The Donegal County Museum, High Road, Letterkenny until July 29th. Scottish Smalls, mini-prints made by artists in print workshops around Scotland, is at Ceardlann na gCroisbhealach until July 29th.