Auckland Libraries has restored 200-year-old Māori sketches - some of the first materials to teach the world about the Māori culture and language.

The ink drawings will be loaned to the Royal Academy of Arts in London in September as part of an exhibition marking 250 years since James Cook's first voyage to the Pacific.

The five sketches date back to 1818 and were drawn by Tūai of Ngāre Raumati and Titeree from Rangihaua in the Far North.

The two young rangatira had been sent to England the previous year by the Christian Mission Society who were keen for the pair to spread the gospel to Māori.

They fell ill in London and were visited by clergyman George Bull who gave them paper and pens.

Auckland Libraries Principal Māori curator Haunui Royal said the drawings reveal the struggles they faced abroad.

"Tūai's older brother was a man called Korokoro, and he was the principal rangatira of Ngāti Raumare, and [Tūai] drew his face and his moko.

"They're miles from home, probably very very homesick, and all these images are probably the things that connected them really closely."

Photo: Sir George Grey Special Collections / Auckland Libraries / GNZ MMS147 drawings

George Bull gave the drawings to William Greenwood who brought them to New Zealand. In 1897 the Greenwood family donated the sketches to the Sir George Grey Heritage Collection.

Mr Royal said pen illustration was almost unknown to Māori at that stage, and the five images held historical and cultural value.

"It's quite extraordinary how good they are and how detailed.

"They drew waka taua, they drew weapons like patu and tiwhatiwha, Tītiree drew some kites."

Photo: Sir George Grey Special Collections / Auckland Libraries / GNZ MMS147 drawings

Auckland Libraries' preservation manager David Ashman asked experts from around the world for advice on restoration techniques for the now brittle paper.

"They're 200 years old, they're unique, and they're really important and so I wanted to make sure that whatever that I do is the best that can be done for these items."

Traditional paper repair techniques weren't suitable because of the risk of spreading corrosive ink further into the paper so special tissue was used to fix damage caused by the original iron gall ink.

"What we came up with was remoistenable tissue. We made that ourselves using a gelatine adhesive and a very fine Japanese tissue."

Mr Royal said the drawings only scratch the surface of the Māori material in the Sir George Grey Collection.

"We have significant whakapapa, Mātauranga Māori, cosmology - from informants like Wiremu Maihi Te Rangikaheke who was a principal informant for Sir George Grey."