Kōyama, not from a potting family, worked at a ceramics factory to pay his way through night school, where he learned potting and firing techniques. In 1969 with his friend Furutani Michio (1946-2000), Kōyama reengineered an anagama kiln to reproduce classical style pottery for the first time in Shigaraki since the medieval era. He was an early experimentor with "mentori waza", facet-cutting his clay surfaces. He first began exhibiting in 1973 with solo shows at Mitsukoshi, Tokyo, and Maruei Art Gallery, Nagoya. Since 1992, he has had exhibitions in The Netherlands, Hamburg, New York, Cleveland, Australia, London, Boston, Philadelphia, Baltimore, and Frankfurt, with numerous exhibitions at Takashimaya in Kyoto, Tokyo and Osaka. Kōyama works in tandem with nature, taking charge of form ceding control to some extent during the firing. Weather, outdoor temperature, presence or absence of moisture in wood all contribute in an anagama to the outcome of surface effects.
Kōyama Yasuhisa has brought the pottery of Shigaraki, a millennium old kiln site, into the modern era. Unexpectedly he does this using the ancient technology of the tunnel kiln (anagama) encouraging the quiet coloration which appears only in an open kiln of this type. His vessels are carved with piano wire as forceful geometric or abstract shapes, and with surfaces which can take on the look of eroded rock walls.