The sale was "uncharted territory" but he believed The Canoe Tainui could fetch $1.4 million to $2m at auction, which would surpass the record $1.33m paid at auction in April for Charles Goldie's A Noble Relic of a Noble Race. The painting last sold for just $550 in 1969 ($8800 in 2016).
Plumbly said Tim and Sherrah Francis bought The Canoe Tainui, which is spread across eight 600mm square boards, as a young married couple in 1969. It was their habit to buy art at the time it was completed, so many pieces in their collection, bought for relatively modest prices, had since soared in value.
"The Canoe Tainui strikes to the heart of what's special about the collection, which is that they bought it in the moment. They got it at a fortuitously cheap price, but I don't think they ever bought a piece with an investment in mind."
The couple lived overseas for several years, including during Tim Francis' stint as New Zealand ambassador to the United States, and the paintings travelled with them. The Canoe Tainui joined the couple in New York and Washington DC, but was only lent to overseas exhibitions twice, Plumbly said.
"They were [considered] a part of the family."
McCahon, who died in 1987, painted The Canoe Tainui after the birth of his grandson.
"His son-in-law was from the Tainui tribe. This really stimulated McCahon's interest in Maoritanga ... and the genealogy of the Tainui people."
The text is based on the genealogy of the tribe and comes from the preface of Matire Kereama's book, The Tail of the Fish: Maori Memories of the Far North.
McCahon wanted people to "experience" his work, rather than simply look at it, and the sheer size of The Canoe Tainui allowed that, Plumbly said. "It's a painting you feel as much as you see ... and that's what he wanted."