AQUA REGIA

[Bruce]

      Aqua regia or nitric and hydrochloric acid mixture: am thinking of this as a stain to use on my curly-maple stock.  Several questions as I do not have experience with these two chemicals in conjuncture with each other before.  1) Which acid is the safe way to add to the other acid (1:1 ratio), i.e., nitric into hydrochloric or vice versa?  2)  What  color is rendered with this stain?

[Dphariss]

Hydrochloric acid in the mix tends to muddy the grain.
You need to the nitric to make the stain.
This was all thought out a very long time ago.
They used nitric acid.
The acid is not the stain. The stain is the ferric nitrate made when iron is added to the nitric accid. The iron solution does the staining. Ferric Nitrate that is essentially acid free will stain wood just fine.
Dan

[jerrywh]

Aqua regia is very nasty stuff. Even opening a bottle of it in the shop will rust everything around it for 6' and for weeks afterwards. I made some of it for doing gold work and after testing it all I wanted to do was get rid of it. I do not want it around my place.  OH I forgot it gets to your lungs , eyes and nasal passages also. Terrible stuff. It doesn't work well either.

[doug]

     strong nitric will colour the wood presumably by oxidizing it.  I think it also leaves corrosive residues in the wood to a much greater degree than when using iron dissolved in nitric or at least I have never had corrosion problems with the nitric and iron mix

cheers Doug

[Bruce]

     Yes, I am familiar with the hazards of working with acids.  I am not a dolt!  However, I seek the results of others who have used this combination of acids.  I have use nitric acid in which I inserted iron filing to arrive at the Aqua Fortis stage and results were beautiful on that specific piece of maple, but this gun-stock, on testing, seems to want to run to brown.  That is not my objective.  So, coming upon the old usage of Aqua  Regia, I interested in what others have experienced on its usage.  Thanks.   BHB

[Benedict]

It seems to me that in similar discussions on this subject, it was mentioned that Wahkon Bay Aquafortis had hydrochloric acid and nitric acid in it.  Doesn't that make it Aqua Regia?  Maybe I misunderstood about Wahkon Bay but that is what I remember.

Bruce

[jerrywh]

when volunteering  to answer your question I didn't realize you already knew so much. Pardon me.
 Please enlighten the rest of us when you are done. 

[Scott Semmel]

The maker of wahkun bay, I believe his last name was Williams, posted this on this board some years ago, it may be in the old archives. All of the products Aqua Fortis, Browning solution and blueing solution were the same matrix in different dilutions, to my eyes the more diluted browning solution  works as well for a stain as the more concentrated Aqua fortis.
"So, here we go... 300 ml (10 fl-oz) of conc HNO3 (15-16 Molar), 240 ml (8 fl-oz.) of conc. HCl (10.5-12 Molar), mix the acids, in large, heat-tolerant container, add about 30 grams (~2 oz.) of 4d finish nails, do this outside, depart the immediate premises and allow the iron to dissolve, liberating NO2 gas, very dangerous, so get out of there, and isolate the system from any metal objects you care for!! Let this exothermic, almost volcanic, reaction occur, allow to cool, then with dionized or distilled water, dilute this matrix to one gallon, or about 3784 ml, total solution. Store final product in amber glass or polyethelene container. This will give you enough browner FOREVER. To make the AQ stain, follow same procedure, except after reaction has ceased, dilute to only about one-third, or to about 1200 ml (~40 fl-oz) of total product or solution. Now, if you are only interested in creating a stock reagent, then one can approach it by taking only the conc. nitric acid, diluting about 2 or 3 to one with water, by adding acid to the water, NEVER, the reverse, and adding degreased steel wool to the acid solution until no more appears to react, then use it for final product in that state of dilution. Pure nitric acid will not dissolve the iron, it must have "excess protons" within the system, whether from another acid, like the HCl, we cited, or from the water, which obviously need not be that pure, as we need H+ ions, not water molecules...
That's the story, not bioengineering or rocket science, but be careful if you undertake this project, as the NO2 is dangerous, noxious, toxic, and some say even carcenogenic... Wear eye protection and rubber gloves when handling any strong oxidants, safety first, stock stain/barrel- browner second!!"

[Dphariss]

The maker of wahkun bay, I believe his last name was Williams, posted this on this board some years ago, it may be in the old archives. All of the products Aqua Fortis, Browning solution and blueing solution were the same matrix in different dilutions, to my eyes the more diluted browning solution  works as well for a stain as the more concentrated Aqua fortis.
"So, here we go... 300 ml (10 fl-oz) of conc HNO3 (15-16 Molar), 240 ml (8 fl-oz.) of conc. HCl (10.5-12 Molar), mix the acids, in large, heat-tolerant container, add about 30 grams (~2 oz.) of 4d finish nails, do this outside, depart the immediate premises and allow the iron to dissolve, liberating NO2 gas, very dangerous, so get out of there, and isolate the system from any metal objects you care for!! Let this exothermic, almost volcanic, reaction occur, allow to cool, then with dionized or distilled water, dilute this matrix to one gallon, or about 3784 ml, total solution. Store final product in amber glass or polyethelene container. This will give you enough browner FOREVER. To make the AQ stain, follow same procedure, except after reaction has ceased, dilute to only about one-third, or to about 1200 ml (~40 fl-oz) of total product or solution. Now, if you are only interested in creating a stock reagent, then one can approach it by taking only the conc. nitric acid, diluting about 2 or 3 to one with water, by adding acid to the water, NEVER, the reverse, and adding degreased steel wool to the acid solution until no more appears to react, then use it for final product in that state of dilution. Pure nitric acid will not dissolve the iron, it must have "excess protons" within the system, whether from another acid, like the HCl, we cited, or from the water, which obviously need not be that pure, as we need H+ ions, not water molecules...
That's the story, not bioengineering or rocket science, but be careful if you undertake this project, as the NO2 is dangerous, noxious, toxic, and some say even carcenogenic... Wear eye protection and rubber gloves when handling any strong oxidants, safety first, stock stain/barrel- browner second!!"

Wakhon Bay "AF"....
This stuff is hard to neutralize and turns stocks BROWN in time.
Like I said using hydrochloric in the mix will screw up the stain job.
The HC was added to make it *easier to make* NOT to make a better stain.
Simply "cutting" the nitric with 20-50% water will allow it to dissolve the steel better. Its still pretty nasty reation initially. I add iron till the acid is near completely/completely depleted. If too strong I add iron after its bottled, but leave the cap loose. Straight nitric is slow to eat the steel in some cases. Water speeds it up, so does HC. But water does not damage the staining quality.
I did find that mixing the WB browner and "AF" made a good rust bluing solution since the brown will stop rusting after about 3 coats on 4140. Adding the stock stain allowed the rusting to continue.

Dan

[Mad Monk]

Dan,

Fumin nitric acid is 86% concentration.  We would not see this grade out of certain industries.

Reagent grade is 69.5 to 70.0% concentration.  This is what I had worked with when Reading Scientific was still in business.

With the 70% stuff.  If I used it straight from the bottle and added large hunks of iron it would just sit there and react very slowly.  Once it worked and the concentration level went down to about 65% the reaction would suddenly get wild.  Even with the Pyrex beaker in a pan of ice water it would almost explode out of the beaker.  There is a point in concentration above which the conversion of the iron to nitrate of iron is very slow.

Diluting reagent grade gets the chemical conversion rate down to a point where it is not too violent and controllable by colling the mass being reacted.

Back when I worked in the lab I played with ferric chloride and ferric nitrate looking at what each produced on the wood.  The ferric nitrate was not nearly as effective in producing the desired iron oxide colors on/in the wood.
This is also a point in how much "active" iron you can get into solution in the stain liquid.  For a given amount ferric chloride does not give as much active iron as does ferric nitrate.

E. Ogre

[Scott Semmel]

In various threads on acid based stains my take is that there have been three reoccurring themes; one "the iron doesn't care or know how it got there" after the acid is driven off, vinegar leaves on its own rather quickly HNO3 is driven off by heat and HLC requires higher temps to be driven off, and after the acid is dissipated the staining is complete, two If the acid isn't neutralized with a base the stain will continue to darken and three the use of HLC to make stain muddies and continues to color after application.
My own experience with acid based iron stains is only ten years and I have always used Waken Bay, store bought or home made, so I have nothing to compare it to. Waken bay was highly mourned when it passed, as I remember, so it must have been widely used thus a sufficient sample should exist to compare the quality of the stain to HNO3 only stain. Is everyone seeing the same results as Dan? If you are I have a half gallon of stain that needs to be diluted to browner.

[Mad Monk]

Scott,

The iron does indeed care how it got there when it comes to the range of colors produced on the wood.  The color array is a function of a number of factors.  When you stain the wood you are creating minute particles of the iron as an oxide, carbonate or hydroxide on the wood.  If you simply convert the stain with a little heat you get one range of colors.  If you continue heating or heat at a higher temperature you get other colors.  The type of caustic material used after staining also alters color patterns.

If you look at the range of iron oxide pigments used in paints you get some idea of the range of colors that can be produced by any of the acid stain methods.

Take the old C.K. Williams pigment company near Easton, PA.  They mined ochre ore above Palmerton.  In the ground the ochre "ore" was grey in color.  When that rock was exposed to the air for any length of time it shifted to a yellow color.  In the late 1800's this C.K. Williams Pigment Companymined yellow ochre out of Neversink Mountain here in Reading.  If you heat this yellow ochre ore above the boiling point of water for several hours you get burnt ochre which is an orange color.

These "ochre" pigments are a limonite iron ore.  About 30 to 35% iron oxide with the remainder being mainly limestone.

Then C. K. Williams began to use spent pickling solution from the large Bethlehem Steel plant at Allentown.  This was hydrochloric acid used to descale and clean steel plates made at the steel mill.  They would then treat the iron rich pickiling solution with a caustic to make iron oxide pigments in a wide range of colors.

The color of iron oxide will change with the number of molecules of water attached to each molecule of iron oxide.
Generally, a yellow oxide will have 7 or 8 molecules of water attached to each molecule of iron oxide.  Drive off some of this and you get brown.  Heat very hot to drive it all off and you get a red iron oxide.  That is the basic thing.  Then the Ph of the caustic used effects it as does the particle size of the iron oxide as it is being precipated out of solution from the water soluble acid metal salt to the water-insoluble oxide, carbonate or hydroxide form.

E. Ogre

[billd]

Ogre
 Does this mean when you use aqua fortis you can make a gun redder by heating it more?

Thanks,
Bill

[Mad Monk]

Bill,

One man I taught how to use the nitrate of iron stain did change the colors from browns and oranges to a more red color.  According to him he had to use a good bit of heat to do it.  The trick is to get enough heat without scorching the wood.

Let me say this.  I looked at a lot of originals that came through Dixon's shop.  most of those that had a red tint to the finish were the result of the finish going red.  Not the stain under the red tinted finish.

Another note here.
When I played with the various caustics to convert the nitrate of iron I did some in solution in a beaker with a stirrer running.  Looking at the thing about pH and iron particle size.  When I used potassium hydroxide (caustic potash) the red was so dark that the wet iron sludge looked black.  Then spread out in a thin film it was a deep ruby red color.  But if you use caustic potash on the stock, after stain application, you may expect to see serious problems if you try to finish the stock with a boiled oil or boiled oil varnish.  The caustic potash left in the stock wood will turned boiled oil into soap.
The one thing I did not try, but should have, was to take this red sludge precipitated out of the solution and see what it looked like on a hunk of figured maple.  I had played with the yellow sludge that forms in the bottom of some batches of nitrate of iron and got some nice yellow and brown stain patterns.  This color I had seen on an orginal half-stock that had been made around 1850 outside of Hagerstown, MD.  It had come down through C.P. Wood's family and when found was still in the original wooden box packed in wood shavings.  Even had the original "tin charger" stuffed in the patchbox.

E. Ogre

[Dphariss]

I suppose the stocks turning browner using Waukon Bay AF  could be a failure to properly neutralize. The stuff is or was pretty acidic. Thought I did everything right but?

Dan