All of the artworks in this catalogue raisonné were created for public display of defined duration. Whilst most of the artist’s works are archived digitally, those archives are simply that - digital records of essentially incorporeal works. There is no art object in the usual sense. There is no 'thing' to collect or conserve. This begs the questions, what/where is the art?

Not unlike many performance artists, Firrell has argued that the art is in the moment of experience. It is only when the artwork is displayed publicly that it is finally animated, has escaped into the 'wild', is ‘alive’, and therefore ‘real’.

In addition, these are not artworks that happen to have been displayed on billboards. They have been created expressly for display on billboards in pursuit of a particular effect in that particular medium in public space.

The logical conclusion of these ideas is that the ephemeral work of art cannot be conserved as we would usually understand the term. For Firrell’s artworks, their respective moments in the light must pass - that was always the artist’s intention - and that temporariness is also an inherent part of the work's character.

This leaves the documentary photograph - a frozen moment of time in which the artwork was publicly witnessed. A good documentary photograph helps us to understand the work itself, but also the work as it appeared at the moment of witness.

The photograph can evoke something of the feeling of the living, disseminated work. The moment can also be referenced, contextualised and confirmed. And so, for the purposes of this catalogue raisonné, this can be an advantage. Rather than referring to an individual artwork by reproducing a facsimile (as would be the case with a painting, for instance), the catalogue can reference the artwork as captured in its moment in the light. The photograph is not a facsimile of anything but a factual documentation of the moment in which the artwork entered and inhabited the public realm.

Photographer Yves Salmon has been of particular importance as photographer of choice, cataloguing more of Firrell’s works over the years than any other single photographer. Her pictures show precisely what the artist said and what the saying of it looked like at the ‘moment of utterance’. The image-making has grown more and more collaborative between artist and photographer over time. The vast majority of photographs in this catalogue raisonné are by Yves Salmon (exceptions are noted otherwise).

At the time of their appearance in public space, the majority of the artworks were accompanied by a ‘digital gallery label’ delivered via mobile device. These labels provided interpretation of the artwork, background about the artist and reference to other works in the series, where applicable.

The narratives offered by this catalogue raisonné are based where possible on the original digital gallery labels, supplemented by any additional information brought to light by the passage of time. Each catalogue entry confirms the details of the commission, its context, date and location of display, the inspiration for the work if that information is available, and who/what was implicated in the making and showing.

Where possible, additional curatorial interpretation is included relating to influences, early prototyping, and unpublished variations of the work with the aim of shedding light on the development of each work in question.

The catalogue is indebted to the photographers who have recorded the artist's work over the decades. Thanks to Bobby Willis, Tom Stuart, William Maughan, Tommy Ga-Ken Wan and Yves Salmon for their documentation of these evanescent fragments of time.