Pick up a spa treatment voucher and you’ll notice something special: a fantasia of tiny liquid crystals that react to the heat of your skin and blossom into stunning colour.
This magical effect is down to the use of a design incorporating thermochromic ink: a material that reacts to changes in temperature to produce vivid patterns which then fade as the paper cools. See this technicolour wizardry first hand, pick up a spa treatment in store or choose from a selection of 11 spa treatments online.
Fairytale-esque it may be, but thermochromic ink developer Mike Parsley PhD assures there’s science behind the magic. As director of research at LCR Hallcrest LTD, a family-owned company pioneering temperature sensitive, colour-changing graphic technology, he’s dedicated his career to researching liquid crystal materials and spends his days concocting strange and wonderful materials in his lab just outside Poole, Dorset.
So just what is thermochromic ink and how does it work? It’s a difficult process to put into layman’s terms, as Mike explains: “The pigment is made up of an oily mixture of organic chemicals which forms a liquid crystal mixture. This reacts to changes in temperature by changing colour. For the best results, the inks need to be freshly made and printed in a well-controlled environment under strict protocols.”
Mike’s lab is a combination of beakers, books and vials of colour that twinkle in the light. On the side, two chocolate fountains have been repurposed and now churn out waterfalls of vivid liquid colour. Here and there, sunlight illuminates inks which blush under the warmth. Mike is busy heating beakers of transparent ink to demonstrate how the contents respond to heat.
“The materials are unique”, he explains, “and it’s hard to promote what we do because it’s not until you get into the lab and see this that you understand. It’s very hands on and when they see it people become interested - almost too interested. 99% of the things people want to do with them, you can’t do.
“When we’ve had success in the past everyone’s been going at 100 miles an hour and these are delicate materials. They’re expensive, extremely sensitive, difficult to use and easy to destroy. A lot of people who have a wonderful idea find it difficult to accept that it can’t be done either technically or economically. Lush’s application is, in many respects, the perfect fit because it’s packaging, and if the ink moves by a degree or two it doesn’t change the overall effect.”
As Lush’s lead designer Gemma-Lea Goodyer explains, the collaboration with LCR Hallcrest has been in the works for a while. “The studio production team did a lot of research and development”, she says, “exploring different applications for both the thermochromic and light reactive inks on bags and gifts packaging. We loved it as a concept, but hadn’t really found the best place to use it effectively.
“Spa seemed like the best fit, as the heat-reactive ink acts as a nice mirror to the ‘touch’ element of massage. It also elevates the act of buying a spa voucher to make it a lot more experiential. Because Lush Spa treatments are much more than simply massages, we didn’t want these gift vouchers to be like those you can just pick up at a till point in a supermarket.”
Once the project was given the go-ahead, Mike explains that bringing the spa vouchers to life was a question of trial and error. A team of seven worked together on concept work, effect demonstrations and pilot-scale manufacturing to ensure the final design was effective, reliable and had the “wow factor”.
“The many variables in the process need to be reduced to just those which directly affect the chances of success,” Mike explains. “They then need to be precisely controlled within the specific ranges for each that will give the best results. For example, deciding the optimum temperature response is an area that needs very careful consideration. The skin temperature on a person's fingertips can vary by a few degrees centigrade depending on whether they are relaxed or stressed and so the complexity is in managing the details.”
Despite the extensive research and complex application of the inks, it’s easy to be simply enchanted by their effects. It’s a bright, sunny day in Mike’s lab and the travelling light paints vivid patterns across thermochromic paper scattered on the desk. Lean on any surface and you’re likely to leave a vivid handprint that flares up and then slowly cools and fades, while vials of brilliant colour bubble and bloom.
Do his children think he’s some kind of magician? Mike laughs. “Kids do seem to be fascinated with the colour changes - they particularly like the colour sheets. My son even did some work experience here - he thinks it's all pretty cool.”
Mike’s own passion for the materials hasn’t faded in 35 years, and he still loves the initial moment a customer experiences the effects firsthand. “It’s when people see something happen that they don’t expect”, he says, “for example, when they touch the ink and the colour-change effect is bright and instant – like the flood-coated, full-coverage prints. If the colour changes can also be made to mean something, for example, using staggered temperature trigger points and multiple prints, more complex messages can be put across.”
Yet Mike also remains quietly protective of the pioneering and volatile ink technology. “It’s a hobby I get to do as a job”, he says, “and we’ve been very conservative really in what we do. We’re a small company. If you added up the total tonnage of these chemicals that have been made throughout all of history, you wouldn’t fill a swimming pool.”
It’s just one of the reasons that, for now, these complex materials remain safely under lock and key in the lab, and Mike remains a gatekeeper to their secrets.
Get your hands on a technicolour treat by picking up a spa treatment in store or online.