black stain

基本解释

In 1873 the Italian scientist Camillo Golgi developed a black stain to highlight the micron-thin neural strands.
1873年，意大利科学家卡米洛·高尔基（Camillo Golgi）发明了一种黑色染料，可以对极细的神经索进行染色。
In a painter's house, I saw a very special painting which was a piece of munted white paper, on the left middle of which there was a black stain.
在画家的房子里，我看到一幅极其特别的画：那是一张经过装裱的白纸，但在其左侧正中有一个黑点。
baicaoyuanrena.blog.163.com
Meanwhile our roaring creek was still at it, but thinner and more quiet now, running from the cliff face itself a mile up the valley in a big black stain I could see in the gray rock.
于此同时我们那轰鸣的溪流依然固我，但它如今变得瘦弱淡静，从一里外山谷上灰暗石头中我能看到的一个黑色大污点，朝崖面飞奔逃离自己。
blog.sina.com.cn

They were, understandably, deeply offensive to black Americans and all others who regard segregation as a terrible stain on this Nation's history.
CENTERFORSECURITYPOLICY: Dustbin Durbin