Start with a soft and large round brush with a 50% opacity.

使用柔软的大号圆形橡皮，并将不透明度设置为50%。

youdao

When you are finished with the shading, use a smudge tool to smooth the surfaces. I use a hard round brush with about 40% strength!

当你结束对暗部的绘制后，要用污迹之类的笔刷来平滑表面。我用的是硬的圆形的笔刷，强度为40%。

youdao

That latter tool, the Advanced Healing Brush, lets you paint in corrections, rather than using the round dropper to make tweaks.

ENGADGET

When his mistake emerged, Bob would have had a metaphorical clip round the ear from the gaffer and would be sent out at first light the next day with brush and paint to correct his mistake.

BBC: Lines painted in early Spring...