underpaint

例句：

1. 1. The artist carefully underpainted the canvas before starting to paint.
   这位艺术家在开始绘画之前仔细地在画布上作底色。
2. 2.The underpainting was so well done that it almost looked like a finished painting.
   这个下笔非常精细，几乎看起来像是一幅完成的画作。
3. 3.She underpainted her drawing with a pencil first, then filled in the details with oil pastels.
   她先用铅笔在画上下笔，然后用油画棒填充细节。