Before you enter the gallery, a notice on the door declares that those with heart pacemakers and other such things be warned that strong forces are present inside the gallery: 'The magnet is always on', it provocatively declares. This is not a piece of braggadocio or tacky advertising claiming a heart-stopping array of art masterpieces but a genuine caution occasioned by Doreen Southwood's work which utilises hundreds of powerful magnets to hold steel washers and bolts to a metallic surface in a design derived from the brocaded curtain fabric found on the artist's grandmother's farm home. The sign on the door is not a boast but I would be sure it was a bit of tongue-in-cheek, were it not for the fact that humour is not something one readily associates with Michael Stevenson Contemporary. However, in this case, a carefully curated, top-notch exhibition showcasing highly regarded artists it undoubtedly is.

According to curator Sophie Perryer: '"In the making: materials and process" presents works by a range of artists who share a deep concern with materials and materiality, as well as a tendency towards obsessive working processes in which these materials are put to use in previously unimagined ways.'

I am not convinced that this is the strongest of curatorial structures, emphasising a coincidental thematic made manifest through working method, rather than anything like a rigorous conceptual framework. Interestingly, and no doubt due in large part to Perryer's diligent and exemplary curatorial collaboration with several of the artists to realise a holistic show, more profound relations do appear.

There is a tension between abstraction and representation that is one of the most interesting intellectual concerns of the works taken as a whole. Guest artist El Anatsui's Fading cloth looks like cloth but clearly isn't. Rhetha Erasmus's The sum of us evokes a marine skeleton (as well as work by Wim Botha) but is also neither. To a greater or lesser extent all 12 artists have expressly used their materials to represent the concrete abstractly.

Alan Alborough's WYSIWYG can be read as a stately enactment of three words that are presented in that catalogue along with lexicographical apparatus from a thesaurus: corrode, stain, observe. Alborough has created a machine that uses metal and brine to form wonderfully ethereal drawings on paper. Two of these are incorporated into the installation on view in the show, lit by fluorescent lights. The transition from an abstract word to an abstract image through a chemical apparatus is a highlight of the show.

As far as the catalogue is concerned, it really is a substantial document that for the most part gives an honest and useful access point to the various components of the exhibition. Unfortunately, there seems to be something wrong with the repro on some of the images that gives them a graininess that is at considerable odds with the aesthetic of the document as a whole and indeed the exhibition itself.

Sandile Zulu's Lines of origin, like Alborough's work, presents traces of a concrete reality; in this case, a line of rope made manifest through the process of scorching. This is not entirely successful conceptually in my view, being more tweely decorative and less evocative than other recent works by this artist. Also the materials listed as 'fire, water, earth, air' create a feel of pretentiousness that is unfortunate given Zulu's pared-down project here.

Another unexpected aspect of the exhibition is the way in which narrative is revealed in these abstracted works: slight scratches on the stainless steel support of Doreen Southwood's masterful Curtain bear testimony to the truly obsessive and hellishly time-consuming nature of this work, so perfectly realised in its present form. Magnets or no, one cannot help but be drawn to this work and its detailed evocation of the past.

The hellishly time-consuming is also given voice by Paul Edmunds's Sieve. As far as I am concerned this is the richest, most thought-provoking and quite simply finest work on the show. Based on a CMYK analysis of a part of a photograph of the early morning sky, it presents 3D hexagons of this colour information by means of sheets of paper from which the shapes (in two dimensions) representing the colour have been cut. Actually, it is more complex than this and my powers of description are not really up to doing this work justice. Let me simply say that it is a breathtaking example of graphic translation. I cannot get the work out of my mind and it still surprises me with unexpected complexities long after I last stood before it. I must add that the last two paragraphs of the artist's text in the catalogue are amongst the most intelligent and honest things I have read by an artist writing of their work in a very long time.

On the other hand Walter Oltmann's Wire tapestry left me somewhat cold, its '4km of aluminium wire of various grades' causing me to ponder whether the parts were not somewhat greater than the whole. Undoubtedly an act of immense labour, the tapestry lacks the artistic presence that one finds so typically in other works by this talented sculptor. In contra-distinction to them, it conveys the obvious toil endured heavily and with little joy. Were this the work of a woman, the dreary labour that it loudly proclaims may have made a powerful statement. As it stands it evokes tediously wasteful masculine time-wasting more than anything else. Maybe that was Oltmann's intention; whether so or not the work remains a stunningly dull piece by a usually sharp-witted and intelligent practitioner.

Dineo Bopape's Growing everyday is an enigmatic piece that seems to have elicited the most diverse opinions from those that I canvassed. Derivative (of Penny Siopis) or highly original; graceful or sloppy; simplistic or challenging: the opinions are significantly divergent. As far as my ability to assess goes, I am astounded by this artist's ability to combine the deadly serious with a frank and self-effacing sense of humour. She is undoubtedly part of the fresh new face of South African art that deals with the seriousness of the existence we see around us with a wickedly sharp wit and the one thing that maybe was most lacking overall in this exhibition: a sense of real compassion for the subject, the viewer and the world. Too many of the works on display emphasise their own labour, seriousness, importance and yes, materiality, over the thing that art ultimately is really, really good at: allowing us to engage.

I must note that the lack of compassion that I observed in much of the exhibition is a conditional reservation: I was also thrilled at the distance and austerity, even haughtiness that many of the works conveyed. After all that I have written, I think I am still at a bit of a loss with this exhibition. It is undoubtedly a brilliant one, expertly curated and beautifully presented. As a whole I still turn over the various works in my mind and see that they are difficult works: hard to access in cases; certainly very hard to present together in a coherent way.

That is a great strength of this exhibition: unlike Oltmann's wire, the whole is greater than the sum of the parts and what is most strange is that the parts are unusually strong. In my opinion this is the finest exhibition yet at Michael Stevenson Contemporary. Sophie Perryer and team have turned the magnet on: expect the crowds to be drawn in. I shall be pushing through them for many more visits yet.