During the painting process, the bottle was held upside down to capture as much light as possible, and sometimes a mirror was used to provide further illumination.
繪畫時，藝匠向光執瓶，探筆入內，將山水、人物、花鳥、蟲魚等題材，一筆筆畫上去。光線不足時，需用鏡子補光。內繪之難，在於它是反著畫。先勾勒前景、細部，再渲染背景，作畫程序和一般繪畫恰好相反。