She began to create works against gold and silver backgrounds in those days. A wave motion series was exhibited in Gallery Brocken, Japan, l994. Water's wave motion is rendered in sumi on a silver background and flame's wave motion is rendered in sumi on a gold background. For example, the work titled "Wave motion of water" expresses the water reflected light of water flowing on the surface of a rocky mountain. It expresses the natural symbolism of Japan's abundant water.
Hiramatsu's overriding theme is light. Silver expresses light with especial naturalism. Silver captures the scene in front of a picture, like a mirror, and the pictorial scene will change with the positions of the viewers. Moreover, if it exhibited in a dark place, it will become black, and white, if exhibited in a bright place. A silver picture shines and changes variously in this way. Because silver is a difficult color to employ, silver pictures hardly exist in this world.
Gold is the light of the sun which illuminates the familiar world, but the silver light of the universe illuminates the moon and the galaxies alike. Furthermore, galaxies are not the stereotypical views of many stars strewn across an empty sky. Indian philosophy says that this universe began when the wind of a fan blew into empty space. This wind is blowing in her galaxy-themed works because their underpinning is the beginning of the universe.
As a small patch of white sand serves to express nature in Kyoto's Ryoan Temple, the Galaxy series expresses the figure of the dynamic universe on a small panel.