staining question

[littlefat]

In the book "the art of building the pennsylvannia longrifle"  pg. 137 it says " Nitric acid produces a yellow to brown range of color, and can be made reddish by the addition of dissolved iron filing" i've tried it mixed with the iron but never knew you could use it with out adding iron.  is this common ? anybody tried it ? doesn"t the Iron give it its color ? 

[keweenaw]

If you just use diluted nitric acid you can get some soft honey colors after heating but you don't get the reds or dark browns.  It might be ok if you wanted to finish a stock with a very light color.  The nitric acid needs to be considerably diluted, probably no more than 10% acid ( I would do some test pieces starting with 5%) to avoid turning the wood into cellulose nitrate.

Tom

[staylor67]

What % nitric acid is Aquafortis?

[keweenaw]

As to the percent nitric in AF, you'll get varying opinions and the remaining nitric acid in the final solution will depend on how much iron is reacted with the acid.  In practice almost all of the nitric acid reacts with the added iron so the end solution has very low concentrations of free acid.   I dilute 1 part nitric with 6 parts of water  and add the iron to that.  Others use a bit more concentrated nitric but it's not the nitric acid which colors the wood, its the ferric nitrate generated by reacting the iron in the acid solution.  In some trials I did I didn't get any better color starting with more concentrated nitric acid so why bother?

Tom

[omark]

daniel, its my understanding that adding water to strong acid can cause an explosion. i guess the acid in car batteries is weak enough to not be a problem.   mark

[Dale Campbell]

Adding water to acid causes the instantaneous generation of a lot of heat. Adding acid to water allows the water to carry off the heat generated.  But in adding water to acid there is so little water to carry away heat that the water boils.  The boiling will splatter concentrated acid all over the area and you and your hands and your face and your eyes. This can look like an explosion, not that you'll be thinking about whether it was more like instant boiling or an explosion.  You'll have other problems at that point.

[JCKelly]

If you do chose to get some nitric acid, I suggest you store it in some outbuilding where rust is of no concern. Like neither workshop nor garage. Over time - weeks, months - the acid fumes you didn't know about or see will rust every bloody thing around.



As far as mixing acid & water - think molten lead, and water. The professor in my first chemistry class, a thousand years ago, had a nice white gauze bandage where his eye had been. Discussed safety with us.

[rich pierce]

Aquafortis of different strengths, with different amounts of iron (A, B, C, and E), applied in single or multiple coats will give a wide variety of results on the same piece of wood.  I test every piece of maple with my various batches to get the color I want.  The purplish ones here (D was first stained with AQF batch C and F was first stained with AQF batch E) have an overwash of potassium permanganate.

[trimegistus]

One other reason for adding the acid to water, is that if  you DO have a splash occur, you have a solution coming at you that is predominately water with some acid in it, as opposed to a solution that is mostly acid with some water. 

[trimegistus]

PS Rich, I love the colors of batch "C", any info as to the approx ratios?

[rich pierce]

I'm a scientist at work but I don't bring it home with me.    I think C was 1/3 nitric acid to 2/3 water, mild steel nails added till exhausted and some sludge formed, a little more water added to de-sludge it.  John Cholin is the real chemist.  I've heard that if it's not red enough, one can wash with hydrogen peroxide after AQF, heating and testing the color with a water wash.  I love/hate the idea that I never know excatly what I'm going to get with AQF.