So, Lush has a factory in Dorset solely dedicated to making bath bombs.
Internally, Lush call it "the ballistics department" (~bombs~ – do you see?). There are over 15 Lush factories in Poole, Dorset. They're hidden on an unassuming industrial estate, about a 10 minute drive from the train station. I smell the factory before I see it – an unmistakeable Lush-y scent.
I meet Dan Scott, the factory manager, at the door, and take a look at the factory's output figures. On 19 October 2015, 182,890 bath bombs were made in the Poole factory – its biggest day so far. "Over 13.5 million bath bombs were made in the whole of 2014," Scott says, "but we are on to better that this year."
As you'd expect, the factory is very glittery. The floor is covered with colourful dust and sparkle. Twenty minutes in, my white trainers are now pink. "People go through loads of pairs of shoes and laces," Scott says.
There's a reason why bath bombs smell so strongly.
The smell is due to the fresh materials, Simon Constantine, Lush's head perfumer and head of ethical buying, says: "Above all else, people smell us first. It's a love/hate thing – some people go, 'Oh I can't go in there, that stinks.'
"The main reason you can smell Lush so strongly is that it's all unpackaged, and we use a lot of natural materials. A lot of people think that it's synthetic, but it's not."
But none of the workers notice the smell any more.
I chat to a packer, Kasia. "I've been here two months now," she says. "When I go home after work, my housemates say, 'Oh, you smell so nice,' but I don't notice the smell any more. I do still notice the smell when I come into work in the morning though."
Most staff start their career on the factory floor. Rachel Lake, our guide, started as a Christmas temp in the factory, and now designs bath bombs in the lab. She points out one of hers with pride – it's called Stardust.
Making a bath bomb is pretty straightforward.
Most bath bombs contain the same basic mix: bicarbonate of soda, citric, colour, and fragrance. In a compounding area, bicarbonate of soda is mixed with colour and fragrance custom to each bath bomb. The compound is then mixed with citric and brought to the assembly line.
The mix takes about 30 minutes, though some bath bombs are more complex. Ahmed on the compounding station explains that Sex Bomb, for example, takes an hour and half due to the complex mixture of colours and fragrances.
Bath bombs made in the Poole factory will go to the UK, Ireland, and some European countries. Elsewhere, Lush have seven manufacturing outposts around the world, catering to local markets.
And each bath bomb is assembled by hand.
To make a bath bomb, you need a dedicated assembly team, ranging from two to 20. The assembly lines vary depending on what's selling best. For example, every day there are 20 people on the Intergalactic station. It shows – about 8,000 Intergalactics are made a day in the Poole factory.
I have a go at assembling the Luxury Lush Pud (a Christmas item) and I muck it up immediately. It's pretty complex – there are several steps, involving proper holly placement. "We'll let you keep that one," Scott mutters helpfully.
All bath bomb inventors have their signature style.
I leave the factory with Lake, and visit the Lush Inventions Lab (above). Jack Constantine, head of product development, and Simon's brother, greets us.
Making bath bombs "is quite an individual thing", he says. "You have a certain style and that shows in each person who makes a bath bomb." Jack came up with the multi-layered bath bomb (think pockets of colour, rather than just one).
Other creators focus on hidden effects within the bath bomb.
"My bath bombs tend to be more pretty," Lake says. "I like not knowing what's going to be on the inside. Like Stardust – you don't know that's going to be in there. And then you have a bath and all these stars start coming out."
Jack feels "it comes down to taste – I can tell when Rachel's working because there's a certain style to them. Like Frozen, or Stardust – they're quite soft and subtle. Mine are more OTT. So I'm quite vivid with it – I like to focus on colours, it always shows in my work.
"Whereas Mum [Mo Constantine, inventor of the Bath Bomb], will be like, bish bash bosh, get it out. She's made some great ones, like Butter Ball, where you've got cocoa butter in it and it's just wedges of cocoa butter."
Bath bombs are tested in a giant sink.
"We need a large surface area to see the effect," Lake says.
"We've done up to 200 bath bombs in one go in this," Jack says. We add the ingredients for 10 Experimenters to the sink, and watch the results. It's mesmerising (above).
Matching the scent to the bath bomb is a technical affair.
"When it comes to perfume in ballistic," head perfumer Simon says, "you've got some technical considerations, i.e. does it fit the theme of the product, make sure the scent doesn't do something weird in the bath, how long will it last, and so on."
And the link between colour and scent is incredibly strong, he says. "I can have worked on a perfume completely independently, and left it in the lab and said it was for a soap, then somebody picks it up and puts it in a bath bomb because they love the smell.
"Or I could get given the name, the concept, the colour etc and be asked to make a scent for it – and it becomes a fusion. It's not like, 'This is the bath bomb, make it smell of violets. Instead it's like, drop it in, have a smell, doesn't actually fit the colour, go away and tweak it."
So, armed with this knowledge, we asked the experts all the bath bomb questions you've always wanted the answers to. Click here to find out more.
Transport to the factory for this piece was provided by Lush.