During the trial the two companies deinked paper waste containing 5% HP Indigo printed paper combined with the standard mix of print waste. 

The HP Indigo prints were made on a variety of coated and uncoated wood-free papers, with a representative range of ink density including high-coverage photo prints. 

According to Arjowiggins research and development director Andrew Findlay, the trial, which was carried out in standard Greenfield Mill process conditions, achieved "saleable, high-quality deinked pulp suitable for coated or uncoated paper production".

He said: "Importantly, mill process efficiencies were unaffected."

Pinni Perlmutter, director of technology at HP Indigo, added: "HP was pleased with this successful deinking result, which involved over 9 tonnes of HP Indigo prints.

"This well-documented trial creates a useful performance benchmark as we continue to research ways of assessing and improving, as needed, HP Indigo print deinkability for a wide range of deinking mill operations."

However, deinking trade body Ingede questioned the value of the trial, because it was carried out at the highly specialised Greenfield site, a Bright White Office Paper mill, rather than at a standard de-inking plant.

Ingede's Axel Fischer said: "These results are interesting, but not surprising. This is not proof that it will work in every mill, this is not a model for a general deinking plant, and it does not change our attitude of the deinkability of Indigo.

"This only means that HP should label Indigo as Indigo paper, collect it and ship it to Arjowiggins but keep it out of the rest of Europe."