Mila Kunis has ''never worked for a better company'' than Gemfields.

The 'Oz The Great And Powerful' actress only signed up to work with the ethical jewellery company because she believed in their message right from the moment she was approached to work with them.

She said: ''There's a difference being part of a family-owned company and being part of a conglomerate - you feel as though you're a part of something, and you don't work for them, you work with them.

''You don't want to endorse something that you don't believe in. I've done that before and it's just one of the hardest jobs to do. Why do it? I believe in this company and I believe in what they stand for. Lesson learned, absolutely.''

Mila - who has previously fronted campaigns for Dior and Gap - was approached by Gemfields' CEO Ian Harebottle, but wouldn't sign up to appear for the gemstone specialists until she was sure the company was transparent and ethically inclined, and she has since paid a visit to their mines in Zambia.

She added to Vogue.co.uk: ''That was absolutely the most important thing. Anything that has to do with stones I think you want to be a little cautious about. ''They opened their doors wide and just said, 'Go ahead'. It was great. They've been so great at letting me be a part of anything and everything I've been able to. I chose them in the same way that they chose me and I have honestly never worked for a better company.''