It has been used for thousands of years as a way to hunt without scaring your prey, or to recognise cultural silences during mourning or to conduct secret conversations.

Key points: More than 10,000 photographs have been collected and sorted as part of the research for the landmark language document

More than 10,000 photographs have been collected and sorted as part of the research for the landmark language document Linguistics expert Dr Bentley James said Yolngu sign language was starting to disappear due to a number of factors

Linguistics expert Dr Bentley James said Yolngu sign language was starting to disappear due to a number of factors Dr James said the team involved with compiling the volume hoped they would have enough funds to finish it this year

Now the ancient art of Yolngu sign language is being documented for a landmark resource, to help prevent this rare form of communication from disappearing altogether.

The "beautiful volume to give back to the children" is being created by anthropology and linguistics expert Dr Bentley James, in concert with senior Yolngu figures and academics.

"I think the first thing to understand about sign languages is they are of themselves a completely separate, full human language, so capable of being able to express the entire gamut of human relations," Dr James said.

"But they run in parallel with the spoken language of the communities, so for example, Yolngu sign language is a language unto itself and so it is in danger of disappearing as many of the other languages in Australia are."

Three generations all practising Yolngu sign language. ( Supplied: David Hancock )

For the past 25 years, Dr James has been studying sign language on Yolngu country in remote East Arnhem Land.

"I found I was drawn to attempting to do something to save Indigenous languages," he said.

His work has entailed living on isolated outstations and in Indigenous communities, learning to speak and sign off patient elders, who have allowed Dr James to write down and document the different words and phrases.

'Nothing like this in the rest of the world'

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 44 seconds 1 m 44 s Bentley James explains Yolngu Sign Language

Now, more than two decades since first embarking on his mission, this extensive volume to hand down to future generations is coming to fruition.

"It is rare, yes, there is absolutely nothing like this in the rest of the world," Dr James said.

"We have collected over 10,000 photographs, of that we have managed to get it down to about 2,500, and those will then express the signs.

"There's 1,800 signs all up, and we've collected about 1,000.

"But in the book we're only using 500 of those signs, so those 2,500 photographs [will be] in full colour, sequential photographs showing the hand shapes, and the movement of the arc and the hand signal itself, and the conventions and how it works."

The volume will also contain a learner's guide and a history of the language, to help people who do not speak Yolngu hand signs to learn how the language works.

Screen time and shifting populations eroding language

Dr Bentley James is developing the Yolngu sign language document for future generations. ( Supplied: David Hancock )

Of the 8,000 or so speakers of Yolngu languages in northeast Arnhem Land, Dr James estimated most were still fluent in sign language.

But, he said, due to the decline of Yolngu people living on homelands and outstations and instead moving into crowded communities, "they're not carrying on their behaviours that they did managing country".

"So they're unable to have opportunity to use sign, there's not much of the hunting that used to go on going on."

Young people being glued to their phones and indulging in excess screen time was also playing a part in the erosion of sign language, he said.

A lack of finances for the project has meant pulling together the book has taken longer than Dr James originally planned, but he said he was hopeful of raising enough funds to have it ready to be distributed this year — the International Year of Indigenous Languages.

"We're doing it at night times, on the weekends, whenever we can squeeze it in we're making it happen bit by bit," he said.

"If we live we will make this book."

He said he hoped to have the document completed by September 23 — the United Nations' International Day of Sign Languages and distribute it to libraries around the nation, "so all Australians can share in this brilliantly valuable piece of our cultural history".