Ogata Kōrin's pair of six-panel screens Irises at Yatsuhashi, a masterpiece of Japanese art of the Edo period, was the object of a multi-analytical investigation campaign. Our study highlighted striking differences between this painting, dating to the period between Kōrin's return to Kyoto in 1709 and his death in 1716, and Irises, a pair of screens on the same subject painted by him around 1701, now in the Nezu Museum in Tokyo. Among the uncommon findings are: the continuous layer of gold leaf extending under all pigment layers (more commonly in this type of painting the areas to be painted were left in reserve, ungilded); the shading of the dark blue azurite in the blossoms with a thin wash of indigo to render the volume of the petals; and last-minute changes in the placement of some iris blossoms over already painted stems and leaves, at variance with the composition originally laid out. Celebrated as minimalist, abstract, and decorative, Irises at Yatsuhashi owes some of its visual impact to how effectively volume is rendered. Kōrin‘s technical choices are behind this effect and constitute the response to the problems inherent in his medium, hide-glue paint over gold leaf. The white ground under the blue affords the painter greater freedom in placing the blossoms to create more dynamic flower arrangements. It also increases the brightness of the blue without affecting its hue. Toning the dark blue with indigo expands the brightness scale in the other direction allowing more efficient volume rendering.