Roman Sushchenko, who denies spying, said Tuesday that he would use unconventional materials, including ketchup, tea, and onion husks, to create reddish and bluish hues, in addition to pencils and ballpoint pens.
"It helped keep me alive," Sushchenko said.
A reporter for Ukrinform, Ukraine's state news agency, Sushchenko was imprisoned from 2016 until his release in September under a Russian-Ukrainian prisoner exchange.
Sushchenko would send his works to his family by mail — with only one depicting the cathedral of Rouen in France, failing to arrive.
He spoke at a news conference organized by the Polish Journalists Association, which is exhibiting reproductions of his works, and the Ukrainian Embassy in Warsaw.
He was based for six years in Paris before his arrest during a visit to Moscow in 2016.
PEN America, which defends free speech and human rights, says on its website that as Ukrinform's Paris correspondent, "Sushchenko not only covered the political, artistic, and cultural life of France but also exposed Russian propaganda in French news outlets."
Speaking to The Associated Press after the conference, he expressed concerns that Russian propaganda seems to be swaying minds in France, even at the highest levels of government.
Sushchenko said he plans to sell the original drawings and donate the money to good causes, including to help the families of political prisoners.