“It didn’t work yesterday, because live chemistry,” says the likeable if mildly disorganised Tim. And “live chemistry” is literally what this show is: flasks, tubes and bottles of mysterious liquids crowd the table in front of him, while lab assistant Alison stands by to help with experiments and show off the results to the crowd. It’s a useful description in another sense too, because this mostly works as a show. Just not always.

Pitched at teens and adults, Rainbows! is a practical science lesson turned into a show, with the emphasis on wonderment rather than the how and why. Loosely themed around the traditional seven colours, the experiments transform clear liquids into vivid shades; whole palettes bloom in test tubes as reactions bubble away. There’s a lot of banter about the risk assessment, reflecting the minor triumph it must have been just to bring this safely to the stage. And the audience responded well to the theatre of it all, oohing and aahing at the visual flourish as the colours swirled around.

But there’s so much more potential still to be catalysed. Tim’s amiable demeanour does much to endear him, but the bumbling-scientist persona isn’t entirely put on, and a little more structure and focus would elevate the show. He could certainly ramp up the drama, build some suspense and anticipation around what we’re about to see. Before embarking on a remarkable demonstration involving strong magnets and aluminium foil, he casually remarks that the magnets are the most dangerous objects on the stage – surely the perfect cue for him to demonstrate why.

There are also a lot of colourful rocks. Tim says he goes round rock shops in his spare time, and I don’t think he’s joking. He does find interesting and surprising ways to highlight their features, but the emphasis on geology leaves little room for optics – a strange choice for a show that’s specifically built around the spectrum. There’s a suspicion that Tim’s included the things he personally finds most interesting, more than he’s genuinely explored his theme.

The interplay between Tim and Alison is genuinely sweet: she’s the sensible practical one who keeps the whole show running, and she carries an air of mild indulgence of Tim’s more puppyish enthusiasm. If they wanted to, they could lean into that warmth, and build their distinctive characters more overtly into the show. As it stands though, this is a fun and heartening way to spend lunchtime at the Fringe, with an atmosphere of collective experimentation and a few striking chemical reveals. It may not quite find the pot of gold, but there’s plenty here to brighten your day.