New Zealand and Chinese scientists are working together on a project that could help deal with China's huge amount of walnut waste and lead to safer hair dyes.

The study to assess damage caused by frequent chemical hair dyeing and find a natural alternative is one of two projects being jointly conducted by Wellington's Victoria University, the New Zealand government's AgResearch institute and Beijing Technology and Business University (BTBU).

BTBU Associate Professor Ying Tang, who completed her doctorate in chemistry at Victoria, said there was a large market for hair dye, especially in China, but there were also health concerns.

"When Asian peoples' hair turns gray, there is a cultural desire to slow and reverse this sign of aging. This creates a huge demand for black or dark brown hair dye," Tang said in a statement from Victoria University of Wellington on Wednesday.

"Frequent dyeing causes many problems and toxicity concerns, so we're trying to find a safe and stable dye that can be used instead of chemical synthetic dyes."

Using dyed human hair, researchers would extract colorants from various plants and expose them to ultraviolet radiation to determine their rate of fading.

"One interesting extract we will examine is walnut. China is the biggest producer of walnuts in the world and disposing of huge amounts of the fruit skins can cause problems, so we're trying to make new use of that waste," said Tang.

The second project would focus on Xuan paper, an ancient Chinese paper handmade from natural ingredients.

The papermaking craft took more than two years to complete, through a process with more than 100 steps, and had been declared an intangible cultural heritage by UNESCO.

By comparing the photostability (resistance to the effects of light) of handmade paper to machine-made paper, the research would determine the rate of deterioration and the chemical factors that contributed to the decline.

"We want to find a way to strengthen the use of Xuan paper because it is very useful to museum conservators and modern calligraphers and painters. There is a lot to learn about how the paper is made and why it is so resilient," said Tang.