He works in oils, pastels, pencil, watercolors, acrylics and collage.
He was working with acrylics in the early years, but around 2005 he changed to watercolours, gouache and oils.
Many of his paintings were painted on canvas with mixed media - oils, acrylics, tempera, conte crayon, ink, whatever was at hand.
He worked in media including pastels and acrylics, and cartoons in various media, and specialist subjects include landscape, steam trains and aircraft.
He mainly relied on acrylics, however, because they dried quickly, enabling him to meet deadlines.
Since the 1960s, acrylics and other plastics have been used as well.
In the 1980s, he left his acrylics to achieve a new softness using oil paints.
Renzi had turned to acrylics in her work on canvas during the 1980s, but then switched back to oil, now treating the layers differently.
