Aqua,
It doesn't matter, either will work. The 10% acetic acid solution might dissolve the iron a little faster and will carry more iron in solution. That will save you applying quite so many coats of stain. I usually use the lower strength, just in case my dog Ollie tangles with a skunk again, so I generally apply stain three or four times, waiting a day or so between applications. No need to "blush" or heat the stock after applying vinegar/iron stain. The acetic acid will evaporate at room temperature and leave behind the iron ions which acquire oxygen from the air and turn into iron oxides. If you stock does not smell like salad the vinegar is gone and the iron is capturing oxygen from the air.
I would NOT use steel wool as an iron source. The steel that is used to make steel wool is really crappy stuff that has all sorts of alloying metals mixed in, some of which turn green and black as oxides. Not good if your want a reddish brown gun.
Maineshop, wash the stock with pure vinegar a couple of times and then let it sit for a few days. You might have gotten a lot of ferrous oxide and it needs some more time to convert to ferric oxide. That can happen if the iron ion concentration gets too high in your stain. Put some of your stain on a wood scrap - let it dry and then put some oil on it. You might find the wood is actually more of a chocolate brown - a mixture of ferrous oxide (black) and ferric oxide (red). If you stock doesn't redden up in a few days get a bottle of hydrogen peroxide and wash the stock with that. Hydrogen peroxide is a strong oxygen donor and can be used to "force" the iron to adopt the ferric oxide form. However, some pieces of wood just want to be brown and its really hard to get them to redden-up.
I hope this helps. And, yes, I was a chemistry major in college.
Best Regards,
JMC
John Cholin
.ood
