"Apparently, it's a couples' bath - you sit in it, and it gets filled with melted chocolate.
"That was it - I came back home with all these new ideas."
Mrs McMaster got to work, creating new products such as a chocolate and honey clay mask, chocolate and goat's milk bath soak, and chocolate and orange healing balm.
Far from exacerbating acne, chocolate can benefit the complexion - with antioxidants helping rehydrate the skin, repair skin cells and increase collagen.
"The antioxidants open up the pores, and create a feel-good, healing effect," Mrs McMaster.
"It feels as beautiful on the skin as it does when you put it in your mouth."
Mrs McMaster began dabbling in skincare after her daughter asked her for some natural remedies.
"Being a mother, I said, 'Of course'. I worked with Dr Google to see what I could come up with.
"I called them my potions without the calories."
She took classes in herbal remedies from Cottage Hill Herbs in Upper Hutt and eventually began selling to clients nationwide.
Her "potions" consist of beeswax - sourced from the 45 hives on her property - olive extract, lavender oil and dragon's blood serum (from tree sap) - as well as "weeds from the side of the road".
She mixes the ingredients in her 40-year-old kitchen whizz.
"My neighbours laugh when they see me on my hands and knees collecting chickweed and colendula flowers.
"My son says he's going to buy me a witch's broom.
"But it's great - I feel like a scientist."
At the expo Mrs McMaster will also do a presentation on chocolate skincare, inviting people to put on the face masks, and try hand and foot exfoliating scrubs with a mochaccino flavour. "Hopefully, people will enjoy getting slathered in chocolate."
For more information on the Chocol'Art expo and Mrs McMaster's presentation go to www.martygirl.com/blogs or www.chocolart.org.nz