Sarah Hamilton (pictured above, right) and her sister and business partner Emily Hamilton were three weeks into launching their first beauty product, Sand & Sky's Porefining Face Mask, when they realised they had a huge problem.

"We were on a flight and by the time we got off, we saw that we'd tripled the previous day's sales," says Hamilton. "It was great, of course, but we couldn't keep up. In the first eight weeks, we sold 60,000 units. We ran out of pink clay – our hero ingredient."