# Zinc screw turning black [closed]

I tried one experiment. I started with ordinal yellow zinc screws.

The screws were sumberged in bath of two parts of $$4.7\%$$ solution of $$\ce{NaClO}$$ and one part $$\ce{NaOH}$$. The screws turned silverish in color. Then, I submerged them into vinegar. Vinegar turned them black. I am now wondering what actually happened. The bath of $$\ce{NaClO}$$ and $$\ce{NaOH}$$ is used to blacken the steel, but it doesn't work with zinc. The vinegar can be used to remove zinc.

But why it was black after that bath?

I was expecting that it would need another bath in $$\ce{NaClO}$$ and $$\ce{NaOH}$$ to become black. Another control screw which wasn't in first bath was just stripped of zinc layer and got a steel color.

• Yellow? Zinc is anything but yellow. Apr 18 at 19:49
• Apr 18 at 19:53
• I still stand by my statement. Certain allows of zinc can look like that; zinc alone can't. Apr 18 at 20:12
• Your zinc is probably an alloy called brass, which is yellow, And brass is made of half zinc, half copper. When dipped into a $\ce{NaClO}$ solution, the copper atoms are oxidized, and transformed into copper oxide $\ce{CuO}$ which is a silverish then black powder Apr 18 at 20:24
• The screws you show are brass. There are many brass alloy compositions, not just half copper and half zinc. You might want to look up brass in wikipedia.
– Ed V
Apr 18 at 20:40