Mr. Fordjour’s position is quite different, both in small matters — he says he turned over 15 works, not 13 — and large: He says he never promised to sell 20 works to the gallery, only that he offered the gallery the opportunity to sell them, and share in the profits.

As the suit once again makes clear, for all the grace and elegance of its product, the art world can be a bare-knuckled place, one filled with all sorts of disputes born of its hefty price tags, unwritten codes and handshake agreements.

On its face, this dispute centers on a technical legal question about whether a 2014 email from Mr. Fordjour to Mr. Blumenthal that outlined the terms of their arrangement constituted a strict sales contract or a different kind of deal, called a consignment agreement.

But it’s also a fight that extends beyond money to touch on the undercurrents of pride, friendship and hurt feelings that can arise over the question of who deserves to take credit for — and profit from — an artist’s success.

In his lawsuit and public statements, Mr. Blumenthal has portrayed Mr. Fordjour as an ungrateful man, one who is now tasting the fruits of recognition and betraying a mentor who took a risk on an aspiring talent.