Once part of Hitler's Reich Chancellery, the pounds 200m site was given to the project by the city of Berlin. "And that's something of a first because we architects are used to getting kicked.". The differences between cultures are often best exemplified by their use of certain untranslatable words or phrases. One such is Vergangenheitsbewaltigung, a key term that underlies the debate that has raged through the otherwise quiet German political and cultural landscape this summer. Literally it means something like "getting over/coping with the past", and since the Second World War has been the central concern of the country's remembrance industry. There's months and months of bureaucracy to get through, city councils, engineers, administrators and architects to deal with.

It's all a long way from the interior life of a studio practice," he says.He has overcome any qualms about public art projects and is now working on two other collaborative schemes with architects in Hackney and Bristol. In Hackney he is about to install a tube of light which changes colour according to wind intensity on the front of a new media centre, while in Bristol he has designed some beacons of light for that city's millennial celebrations.The people of Birmingham seem pleased with the outcome: "I haven't heard anything from anywhere which is negative, it's all been favourable," says Perry. Although enthusiastic about the outcome, he does have reservations about the process of achieving it."The problem with working in the public realm as an artist is that you have an idea and don't see it realized for three or four years. The artists have to be involved from early on, it is undesirable to stick the art on at the end, that hardly ever works," she says.In the case of Tyseley, Ray Perry had the necessary amount of generosity to allow Richman's involvement with the project to cause a number of fundamental changes to the external appearance of the incinerator, and that was before he set to work on coming up with a lighting programme for it - a dramatic moving light show."Martin introduced the idea of red - to highlight the function of the building and its heat - so we changed the yellow cladding to red. He also introduced areas of translucent and transparent cladding to show the internal lighting," says Perry.Although Richman had worked with architects on projects in the past, Tyseley was the first time he had worked on a building from scratch and had such a large input into its final appearance. It is a charitable consultancy which aims to bring collaborative work to a wider audience than that which visits art galleries. Accordingly, it organises installations, temporary schemes and acts as a matchmaker for permanent building projects."Collaboration is becoming extremely fashionable but it is nevertheless a process full of pitfalls - sometimes there is too much territorial jealousy involved and sometimes the relationship just implodes," she says."Collaboration requires an enormous amount of generosity and time.

The council's suggestion for involving an artist was enthusiastically taken up by the client and the architects, according to project architect Ray Perry. The only problem was deciding on a suitable art form."We felt that a sculpture, fountain or painting would be inappropriate for what is a private building on a very public site and came up instead with the idea of external lighting," he says. Having decided on the appropriate form of art for their "industrial cathedral", the architects set about trying to find a suitable artist. They approached the Public Art Commissions Agency, which arranged a slide show of 30 artists who work with light.

From that, they selected six who were given a set of plans for the new building and asked to present their ideas at an interview. Richman was picked, according to Perry, because he was "on the right wave-length for the type of building we had".Getting the right match of architect and artist is absolutely crucial to the success of the project, according to Vivien Lovell, who is the director of the Public Art Commissions Agency. The incinerator, which has an 85m-high chimney, was designed by Derby architects Faulks Perry Culley and Rech and the London-based artist Martin Richman. We weren't put together as a lottery project and were doing it before all that public arts stuff."Various organisations now promote artist/architect collaborations, including the Royal Society of Arts with its Art for Architecture programme and Birmingham City Council which has a "per cent for art" initiative, whereby one per cent of a new building's total cost is spent on an art work for it.One product of this initiative is the city's new incinerator at Tyseley, which burns household waste and generates electricity from the heat produced. "There are lots of people at Tottenham Hale waiting for buses, trains and at the traffic lights and that can be a bit boring. The idea was to give them something fun to look at but not too obvious. So it takes time to work out that the fountain's a clock and more time to work out what time it is," says Lyall.Like McLean, and perhaps influenced by him, he is very clear about how collaborations work most effectively: "The way I feel about the best collaborations is that we start with a blank sheet of paper and work together in free form and what results is something which neither would have thought of separately.

I like working with artists because they have a different eye and way of thinking. But some collaborations don't work if the chemistry isn't there or it is one-sided."Lyall is also critical of other architects who aren't keen on getting involved: "Some architects, even some very famous architects, are a bit strange about involving artists on their projects, believing they are the only creative talent, which is very arrogant and also missing an opportunity by being unnecessarily neurotic about the ownership of creative ideas." But there are enough architects around who are enthusiastic about the possibilities offered - aside from Alsop and Lyall, McLean alone has worked with David Chipperfield in Bristol and Tokyo and is currently designing a new foreshore for Bridlington with Rayner Banham.What started for McLean and Alsop as an experiment and a bit of fun has since been formalised and become more mainstream, McLean suggests: "Will and I started in a real way. It's certainly not art for art's sake."At Tottenham Hale, McLean and Lyall have come up with a new concourse and Underground station - schemes which complement the mainline station which McLean, Lyall and Alsop designed together in 1991. Lyall says it was a collaborative process: "We spent lots of Sundays at his studio brainstorming before editing them down and settling on the actual designs."What they developed for the Tottenham Hale concourse are three separate pieces: a 16m-high lit beacon (the Tower of Time), a fountain (the Bridge of Signs) and some paving, which incorporates writing by local children (the Path of the People).