* Jewellers give twist to classic designs
* Rhodium, ruthenium plate favoured for deep colour
By Jan Harvey
LONDON, May (Reuters) - Ice-white platinum has long had enduring appeal in jewellery and experimental designers are now also turning to its lesser-known sister metals rhodium and ruthenium to produce work in darker hues.
The deep gunmetal finish of black rhodium plate and the pure black of ruthenium are both becoming increasingly popular, jewellers say.
London-based designer Alex Monroe has used black rhodium to plate pieces in his nautically-inspired Beyond the Sea collection, along with silver, and rose and yellow gold.
He has used black ruthenium to create jet black crow's feathers for a 2009 line, and in special editions of floral-themed lines to give a "contrast to the femininity of the pieces," said his firm's chief operating officer Emma Burgin.
Platinum's sister metals are produced mainly for industrial uses: rhodium as a component in automobile catalytic converters and ruthenium for electronics. But demand for jewellery, even when tiny overall, can add to the lustre of a precious metal, especially as the exotic metals become more affordable.
Both rhodium RHOD-LON and ruthenium RUTH-LON are much less expensive than they used to be, with rhodium currently just cheaper than platinum at $1,125 an ounce versus more than $10,000 an ounce back in 2008, and ruthenium at $48 an ounce, compared to $880 at its 2007 peak.
They have appeared in pieces sold by established brands like Tiffany and Links of London. For smaller designers they offer a chance to make one-offs and pieces that stand out.
"It's a little bit more unusual," jeweller Thomas Nayler said of black ruthenium. "I've used it before in bespoke pieces, when customers wanted a particular finish. It looks lovely - a glossy, polished black."
Rhodium is normally white, and commonly used for years as plate to give a lustrous finish to white gold. Black rhodium is made by adding an ink dye that binds to the metal.
Its extreme hardness and high melting point make it a difficult metal for jewellers to work, so pure rhodium jewellery is highly unusual.
Jeweller Harriet Kelsall has been using more and more black rhodium plating in her designs to give her pieces a deep gunmetal finish.
"We have certain chainmail, one-off pieces coming into our collection, and we've been using variegated black rhodium on those, because it's just coming into fashion now," Kelsall said. (Reporting by Jan Harvey; Editing by Veronica Brown and Peter Graff)