Viradon is a direct toner: you immerse the finished print directly into the toner working solution. This works fine with most papers but not with Ilford MG IV. It hardly reacts with viradon.
Indirect toning is using a bleaching agent (i used a potassiumferricyanide solution but other agents are possible) to bleach out the print and then toning in viradon. Gives a nice and subtle result.