Fun with Nitric Acid (Staining Curly Maple)

[joehenz]

We had some Nitric Acid sitting idle at the Lab where I work, so I mixed up a 10% Solution and tried it on a scrap piece of curly maple. Put it on and heated it up with a heat gun until it blushed red. Really brought out the shimmer!

However, when I neutralized the acid by scrubbing the board with a baking soda solution and then rinsing with water, I noticed the baking soda had given the board a greenish cast. You can really see it in this photo where the baking soda got on some of the untreated wood.

In addition to the greenish cast, the baking soda seemed to reduce the shimmer (chatoancy?) some too.

I was bummed out about all that, so I got to thinking that maybe neutralizing the acid wasn't necessary, since I'm heating and basically boiling it all away with the heat gun. So I did an experiment: I sanded two nails to expose fresh steel, and laid one nail on untreated maple and the other on nitric acid treated but un-neutralized maple. I left them in my hot but dry garage for a week. After a week the nail on the untreated board was still shiny, but the nail on the acid-treated board was rusty. So my theory was wrong. :td:

Anyone else seen this? I'm wondering if I add a couple drops of red stain to the finish if I can kill the green? Also wondering if the nail would still rust if I didn't neutralize the acid but put the finish on it to seal it?

 

[rich pierce]

Nitric acid is technically aquafortis, for sure, but the solution folks use to stain rifles is saturated with iron. Make the 10% or up to 25% solution, add iron shavings or small nails, let it cook uncovered until it is done consuming iron. Filter through a coffee filter, etc, and use this to stain maple. Blushing required. Much of the acid is consumed in making ferric nitrate which gives the rusty (red-brown) color desired.

 

[necchi]

And, the greenish tint left is from not getting the wood hot enough while blushing.
The varied shades are due to the properties of the individual peice of maple.

 

[F.G. Ford]

I really did not know the cause of the greenish tint. Thank you for that valued bit of information.
Added note, how soon should you heat ( blush ) after acid staining?
Fred

 

[necchi]

I learned that heating deal here back in 09`; http://www.muzzleloadingforum.com/fusionbb/showtopic.php?tid/235146/post/728639/hl//fromsearch/1/

I wait until the solution is dried and none of the stock or wood item shows any sign of the Aqua Fortis looking wet,, Know what I mean?
The "wash" should look even across the entire piece.
1/2 hour to an hour is usually sufficient for me.

Some guy's will even give it a second wash of solution before the blush.

The neutralizing phase really has to do with stopping the acid from continuing it's work on the wood.
Some use Baking Soda and others Ammonia.
I've found Ammonia to be the most reliable.
If nothing is done the wood can continue getting darker even after the finish coat is applied. It can be a slow action and go on for years.
So you have a nice finish,, 5 years later it's really dark heading towards black,,

 

[F.G. Ford]

Thank you for the response and information
All the best
Fred

 

[talkingamoeba]

Do you use straight household ammonia or is it diluted?

 

[jdkerstetter]

When I use amonia it is the stuff from the grocery store. Diluted? I never bother to read the label. It works fine.

On a side note, I keep reaing post here where people seem overly concerned with raising the grain on the wood as if it is undesirable. I will keep raising the grain and "wiskering" until it won't any more. (Even alcohol will raise the grain some.) I find that I end up with a smooth hard surface. I want to reach that point before I apply final finish.

Enjoy, J.D.

 

[necchi]

Just what jd said,
Glad you mentioned the "whiskering" issue too, just whisker first till the wood is done,,

 

[jdkerstetter]

I knew I wasn't alone but it never seems to come up on this forum.

I want to raise as much grain as I can once the stock is shaped. I'm no carver, but if there is any carving involved you can run into nightmares if the grain raises all over after you are done. Good luck in all those nooks and crannies! :shake:

I want it dead smooth!

Enjoy, J.D.

 

[LaBonte]

1) scraping rather than sanding will help prevent whiskers and scraping was the more common method in the 18th and early 19th Century

2) After applying the AQF burnish the wood - I use antler or bone for this followed by coarse cloth, but one can also use the Scotchbrite type pads which will cut whiskers and burnish at the same time.

 

[Bill Hall]

You don't use straight nitric acid to stain wood. Like already mentioned, it is mixed with iron until it is "used up", and the acid reaction is pretty much finished. Once the solution is saturated with iron, there is no more ion exchange between the two ingredients, so the acid is no longer an "agent", it is now a "reagent".

I noticed your wood seemed a little lighter in color that it would have been if true aquafortis had been used. When the correct solution of acid/iron/water is used, the wood should take on a darker reddish color (feakin' beautiful if you ask me :grin: ).

Even though the acid is considered to be "killed", if not neutralized, it can still continue to darken the wood as time goes by. I learned this the hard way :redface: . I use a baking soda paste, left on the wood for about five minutes. So far it has worked great for me, with no blotchy spots or inconsistencies in the color. Bill

 

[rja72]

I was testing a piece for the first time with Aquafortis. Very pleased with the result. I rubbed on some BLO. Is it normally this dark?
http://i1271.photobucket.com/albums/jj637/rja72/Curley Maple/01e88b16.jpg http://i1271.photobucket.com/albums/jj637/rja72/Curley Maple/4af91775.jpg

 

[Bill Hall]

Looks typical. Some pieces of wood will be a little lighter, sometimes even darker.

You can cut the solution down with water to get a lighter shade if so desired. Just test on a scrap piece of wood from the same stock. Bill

 

[jdkerstetter]

Nice color there. Enjoy, J.D.

 

[Paul R]

When it came time to finish my latest build, it seemed that the only way for me to acquire AF was to be a school or be willing to set up an account & order $200 worth of the stuff. While running around on the internet, I found a site that listed a number of formulas (sorry, I can't find my way back again) colouring different metals different colours. That got me wondering what was in the 'black patina' solution I had used to colour the lead on a leaded glass panel. Lable said 'contains nitric acid. So, tried some on scraps of maple & got some interesting results. Then put some old rusty cut nails in some for a while & results got even better. I don't know what is in the original solution, but I ended up with a very nice chocolate brown stock. YRMV.
I know, a picture is required, but once I get a little less busy working up a load for my moose hunting trip, I'll have to try my luck with posting pictures.
Paul