I've used this ebonizing technique several times. It is a great way to get an ebony look.  
I will add one tip that I found helps to get a finer surface finish.  Because you cannot sand it after applying the solution without risking taking it back to bare wood, I usually wet the material after sanding to raise the grain and then sand it to final grit before applying the solution.  This reduces the the amount of raise grain that solution causes.  After after the solution is dry, I burnish it with a coarse shop towel wrapped around  something hard like a wood block before applying a top finish.  

I've used the steel/vinegar before on some red oak and got a deep black that rivaled ebony when shellac was applied.

Recently I needed to de-rust some steel tubing for some gates I'm making. Gallon of 5% white vinegar and water to fill a 4" pvc capped pipe (6' long), slide in the steel and let marinate for a day. 
Steel is super clean and I've enough ebonizing solution for a lifetime!.

I've had the solution stop working if it sits around for a couple of years.  Not sure if the container just wasn't sealed or what.  

i have holes punched in my lid did not know it needs to be sealed 

Not sure if it has to be sealed but you do not want an open container of this near any metal because it could cause corrosion.  

I’ve had good results with vinegar and steel wool too. But a lot of it has to do with how much tannin is in the wood…so certain woods ebonized way better than others. It’s a great trick to keep in your packet though!

To really get the black as Ryan suggests, tannins are needed to create the color. Some woods (oak for sure) are loaded with it, but if not, some strong tea brushed in followed with the steel/vinegar will certainly react.