# Why does nital need alcohol when etching metals?

I was reading about HNO3 and I saw it can be mixed with alcohol to form "nital", which is useful when etching metals, especially carbon steel.

I wonder why alcohol is needed? HNO3 itself is corrosive for metals. So I did a little search and some college students claimed that alcohol is for holding back the reaction rate to get a better result, but it raised more questions for me... My thought now is alcohol is not as polar as water, so HNO3 would probably be less readily dissociated. But I can't figure out the rest.

• Speculation, it might not be the answer: The alcohol may remove grease and other lipophilic matter sitting on the surface, thus easing the access of the aqueous solution of $\ce{HNO3}$ to the metal. – Buttonwood Jun 24 '20 at 16:14
• I thought it would form alkyl nitrates too. The term nital seems to be the name of the solution, not some functional group. It's said to be used a lot in etching industry, so I guess it works somehow...some also mentioned it's dangerous and can be explosive when made. I'm more interested in what role does alcohol play. – Wang Jun 24 '20 at 18:14
• OK, I found it, but it'd be good if you put some reference in future posts. – Mithoron Jun 24 '20 at 19:10
• So-called “nital” is commonly used to etch iron-nickel meteorites to display the characteristic etch patterns. But @Mithoron is indeed correct. I have always assumed the ethanol or methanol served to prevent passivation of the iron or steel or Fe-Ni meteorite. No clue how, but this should not be done without all the safety precautions and PPE. – Ed V Jun 24 '20 at 19:11