Some of my thoughts re: aqua fortis
First off I am not a chemist but I have asked a friend who is to help me with some of this. Any misunderstanding of his explanations are my fault, but I believe I understand this enough to present it here in some what of a coherent fashion. If any of my chemistry is wrong and any one of you can show me in what way it is wrong please set it straight.
Anyway I have also been pondering the question of the 18th/early 19th Century "aqua fortis".
As an example I present the following two formulae for aqua fortis which are from : "Shepherds' Compleat Early Nineteenth Century Woodworker"
“Common aquafortis” “Take nitre, and green vitriol, not calcined, each 6 lbs. green vitriol, calcined 2 lbs. Distill.”
“Simple aquafortis” “take of green vitriol 2 lbs. nitre 1 lb. Distil
One thing that I have been found is that after much research into pre-mid 19th century chemical terms is that "nitre" - one of the two components mentioned in not only the above two recipes but in most others - is most often listed in period resources as being Potassium Nitrate (KNO3) aka saltpeter and not nitric acid (post mid 19th sources do seem to use the term "nitre" for both, but period resources usually refer to nitric acid "spirit of nitre". But to add to the confusion some resources also list nitric acid as being aqua fortis with no additional ingredients.AUUUGH! (one resource for chemical terms that has links to others is:
http://web.lemoyne.edu/~giunta/archema.html )
1) With that said let's consider salt peter as the possible "original" nitre as listed in the formulae. It is not only a naturally occurring substance, but is also a by product of animal waste, and more importantly it is a strong oxidizer and is the chief constituent of black powder.
2) The second ingredient mentioned is Green Vitriol - aka ferrous sulfate. What is ferrous sulfate? Ferrous sulfate is a by product of the oxidation of iron pyrite or it can be produced by treating iron with sulphuric acid.
Where does one find iron pyrite -
"Pyrite is a frequent associate of all sorts of metal ores. It is common in coal, and in slates and other metamorphic rocks."
"Although pyrite is common and contains a high percentage of iron, it has never been used as a significant source of iron. Iron oxides such as hematite and magnetite, are the primary iron ores. Pyrite is not as economical as these ores possibly due to their tendency to form larger concentrations of more easily mined material. Pyrite would be a potential source of iron if these ores should become scarce. Pyrite has been mined for its sulfur content though. During WWII, sulfur was in demand as a strategic chemical and North American native sulfur mines were drying up. A sulfide deposit near Ducktown Tenn. was found to be able to mine pyrite and other sulfides such as pyrrhotite and pentlandite and produce the needed sulfur as well as iron and other metals."
First method: Oxidation of pyrite can be a naturally occurring process or a man made process in which water (H2O) leaches through the pyrites and when it does ferrous sulfate and sulphuric acid are produced.
Second Method: where would they get sulphuric acid?
"In the 17th century, the German-Dutch chemist Johann Glauber prepared sulfuric acid by burning sulfur together with saltpeter (potassium nitrate, KNO3), in the presence of steam. As the saltpeter decomposes, it oxidizes the sulfur to SO3, which combines with water to produce sulfuric acid. In 1736, Joshua Ward, a London pharmacist, used this method to begin the first large-scale production of sulfuric acid.
In 1746 in Birmingham, John Roebuck began producing sulfuric acid this way in lead-lined chambers, which were stronger, less expensive, and could be made larger than the glass containers which had been used previously. This lead chamber process allowed the effective industrialization of sulfuric acid production, and with several refinements remained the standard method of production for almost two centuries."
Hmmm once again salt peter rears it's hoary head and along with it comes a second component of black powder - sulphur which is a major constituent of iron pyrite!
So based on the above I submit that salt peter and sulphur - two of the components of black powder - may have been either the direct components or used to produce the components of the "original" aqua fortis reagent as used by the gunsmiths of old. There is after all a certain logic to using the same chemicals that were used to produce the black powder which powered the firearms one was making.
FWIW: Eric Kettenburg, who has probably studied the subject of early gun finishes more in depth that just about anyone has stated that there are plenty of citations for AQF being available even in the back country.
Regarding Capt Chee's earlier post quoting Don Newel''s excellent book:
1) Don Newell's book was first printed in 1949 not earlier. That was during the heyday of post WW2 home gun smithing and much of the information had been passed down but from how far back is often difficult to say.
2) Regarding the three brown stains:
A. The first using logwood is a pretty good possibility for dating back to the 18th century, but without citation is left up in the air.
B. The second not so possible, although potassium permanganate was know in the 18th Century it wasn't widely available until around 1830.
C. Nitric Acid and Iron is aquafortis.
Regarding linseed oil - the modern "boiled" hardware variety is nothing like the real properly boiled heat polymerized linseed oil and will dry completely when properly applied. Secondly up until the mid-1800's, most linseed oil was used in conjunction with various rosins and turpentines along with a lead dryer to produce a varnish and was not applied alone as is often done today in the idea that oil was the major American stock finish pre-1850.
Anyway as always an interesting conversation.....
and FWIW an excellent variation of Aqua Fortis can be made using two widely available period materials - apple cider vinegar and iron filings aka ferric acetate - a staing that was used as far back as Roman time for leather and wood. It's good and works similar to AQF (ferric nitrate), but in my experience vinegar/iron doesn't give quite as deep an opalescence to the wood as does AQF.