I think it's true to say that the best design considers itself a metaphor – for the characters' situation or the author's intentions. The Glass Menagerie is an autobiographical piece about Tennessee Williams' family, who were isolated in real life and are also marooned in his memory. In our production we have the family's home – a first floor apartment in St Louis in 1939 - in a big empty black space, like a void. On the stage is a big lake, filled with black liquid, and on it are three lily pads; wooden rooms floating on top of it.

From above, the liquid looks like a mirror, it reflects them perfectly if they look down at it. It is viscous and it doesn't move quite as much as water does - it looks like oil. It's very simple really, onstage there's a sofa, a carpet, a table and chairs for eating; only the props that they need to handle.

We've made it so that the wings to the side of the stage are completely cut off. The only way you can get into the flat is through the scenery. There's a fire escape that leads up to them, which comes up from underneath the stage, but the actors can't traverse the water around it. Everything is marooned onstage, like they are in the narrator's memory.

The fire escape onstage towers up to a vanishing point. In the play, Tom's sister Laura has a collection of glass figurines and in this version the director John Tiffany has only the one glass animal onstage – the unicorn. He's reduced everything to its essence. The fire escape resembles the horn of the unicorn.

We came up with the designs for the show very quickly. John and I were in New York having opened Once the Musical. I had never designed The Glass Menagerie before and John had never directed it. We took a train to Boston for three and a half hours to the workshop of the show and by the time we arrived we knew exactly what we wanted to do and that's literally what's onstage here at the King's Theatre, two years later.

I enjoy making simple designs, but it is a harder to do because you don't want to throw the baby out with the bath water. Simple is difficult, but it is what Tennessee demands. The play is about the unreliability of memory and it also taps into the themes of memory, abandonment and betrayal. The Glass Menagerie is riven with guilt because he left his sister behind. In his opening speech the character Tom goes back in time. He stumbles into the room and the play begins and then he leaves them at the end. We have them there just floating in time. It's a beautiful play.

The Glass Menagerie runs at the King's Theatre in Edinburgh until 21 August.

Read our review of the show here

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