Selina Thompson in salt.
Selina Thompson in salt.

Selina Thompson is taking a sledgehammer and smashing up a great hunk of pinkish salt; she's also smashing at the concepts of "imperialism, capitalism, racism". Yep, the big stuff – and she's going for it, in a show that head-on tackles Europe's involvement in the slave trade. But for all that she is literally wielding a sledgehammer, salt. is a subtle and nuanced production.

The vast welling of rage that prompted Thompson – a 27 year-old black woman from Birmingham – to make the show is focussed into an intelligent, probing performance. She's calm, although we sure as hell still feel her fury. And her measured delivery moves into something more rhythmic and poetic, as she recounts the constant racism she encounters, from micro-aggressions to huge great structural ones.

Thompson embarks on a journey, boarding a cargo ship and retracing the slave trade triangle – travelling to Ghana, then to Jamaica, where both her biological and adopted parents came from, then back to England.

This journey offers no easy answers or trite life lessons; Thompson is exposingly honest about how arduous it is. Salt, she tells us, has healing properties – but at first, its more like opening up the wounds and rubbing it in. On the ship, even as she's reading about the horrors of slavery, she is confronted by the shockingly bald, crude racism of the Italian captain – or ‘master', as he is queasily known – who refers to her as a nigger. Weeks stuck on the boat, in a cabin with no windows, send her stir crazy. She cannot speak to her family at home. She is – literally and metaphorically – at sea.

But when she gets to where her ancestors come from, there's no magical resolution either. She's moved in Ghana and rests in Jamaica, nourished by its fecundity. But with no family there to visit or connect with, she also feels her rootlessness. "So much of the diaspora is looking for home in a places and people where you can't belong," she realises.

Thompson concludes with a commitment to live – and to live with the pain. As well as confronting personal grief, salt. also offers a powerful, potent reminder to its audiences – at the fringe, largely white – of the history of our continent: "Europe is awash with blood, built on suffering," she says. And how that history still manifests itself in ways we may prefer to be comfortably blind to today.

salt. is at Summerhall until 26 August, at 14.30.

For all our content from this year's Edinburgh Festival click here