Butter of Antimony?

[Joe S]

I've been doing a little research on historical browning solutions, and I have some questions that I'm hoping someone on this site can answer.  Until I started this research, the only browning solutions I was aware of were aqua fortis and aqua regis.   I am finding that these were by no means the only browning solutions available, and may not have even been the most common.

I'm doing all my research on the net, which has some limitations.  Although I am aware that there are very early historical references to browning gun barrels, the earliest formula I can find for browning solutions on the net is 1807 (The Monthly magazine; or, British Register, No. XIII, page 316).  This reference recommends aqua fortis or "fpirit of falt" (spirit of salt is hydrochloric acid.) 

Those old boys were pretty good chemists, and by 1811 the British army was using a recipe with five ingredients as follows:

Nitric Acid                  1/2 ounce
Sweet Spirit of Nitre  1/2 ditto.
Spirits of Wine           1 ditto.
Blue Vitriol                 2 ditto
Tincture of Steel        1 ditto.

This was followed with a three ingredient varnish, which rather surprisingly included dragon's blood.

One formula that interested me uses sal ammoniac (ammonium chloride).  The earliest citation for using sal ammoniac that I can find is 1920 (CW Sawyer, Our Guns).  Sawyer states that sal ammoniac was used by "American backwoodsmen" for browning gun barrels.  Sal ammoniac would have been available during the colonial period.  Is anyone aware of any reference to its use during this period?

(Digression:  Sal ammoniac.... So called because it was originally made from the soot from camel's dung at the temple of Jupiter Ammon in Africa.)

Another formula calls for Butter of Antimony, which is antimony trichloride mixed with olive oil (usually) or actual butter (one reference).  According to some references, butter of antimony was used to brown the barrels of the Brown Bess.  Throughout the 1800's, and as late as the 1890's, butter of antimony is cited by several authors as the most common method used for browning barrels.

(Digression - antimony has been known since antiquity:  The Book of Enoch, the great-grandfather of Noah, states in Chapter 8, Verse 1, "And Azazel (an angel) taught men to make swords and knives and shields and breastplates and made known to them the metals (of the earth) and the art of working them, and bracelets, and ornaments and the use of antimony.")

I have two questions about butter of antimony.  First, is anyone aware of any references documenting its use by early gunsmiths?  Second, I am a little concerned about its protential toxicity.  Is making and using butter of antimony a reasonable thing for us home based gunsmiths?

[Dphariss]

If they had nitric acid for stock stain or if their stock stain was fairly acidic they really did not need much else.
I ordered up some Ammonium Chloride crystals and mixed them up in some water and got no reaction on steel at all.
But I was thinking this was how it might have been used, if it was, by early American gun makers.

Dan

[Joe S]

Sal ammoniac process from Angier: 

"Without boiling.  A 0.5% solution produced a satisfactory brownish-black after 5 or 6 passes.

With boiling.  ...the author obtained a very fine deep black finish after three passes with a 2% sal ammoniac solution....sal ammoniac will produce as deep a black as can be obtained by any means."

I haven't tried it myself, so I don't have an opinion about it.  We differentiate browning from blueing processes, but older references seem to call all color change in metal "browning".

[keweenaw]

antimony trichloride is a nasty substance. 

The MSDS sheet lists the following:
Health Rating: 3 - Severe (Life)
Flammability Rating: 0 - None
Reactivity Rating: 2 - Moderate
Contact Rating: 4 - Extreme (Corrosive)
Lab Protective Equip: GOGGLES; LAB COAT; PROPER GLOVES
Storage Color Code: White (Corrosive)

It gives this about specific toxicity:
Oral rat LD50: 525 mg/kg

The approved contact limits are:
-OSHA Permissible Exposure Limit (PEL):
0.5 mg (Sb)/m3 (TWA)
-ACGIH Threshold Limit Value (TLV):
0.5 mg(Sb)/m3 (TWA)

Putting the stuff in butter or oil would limit the amount that could be airborne but would make cleaning it up much more difficult, i.e. toxic grease everywhere.

Many safer ways to make things brown.

Tom

[Joe S]

Thanks Tom.  I've also found that it is teratogenic and also a potential carcinogen.  We used to do things with heavy metals that we don't do anymore.  Mercury comes to mind.  I'm thinking I'll file this one under historical curiosities, and leave it at that.

[heinz]

Salamoniac, or ammonium chloride works very well for browning barrels.  Hacker Martin and others reported it as an old time browning agent.  It is a good flux for silver soldering and a very good flux for soft soldering iron.  It used to come in small bars about the size of a bar of soap for shop use.  I have used it on a number of rifle barrels and like the results.   I think it likely to have been used in the old time gunsmiths shop but would defer to Gary Brumfield and others on that call.

[Mad Monk]

Regarding salamoniac.

I used it for a number of years to brown both ml barrels and iron wire I used in pick and brush sets.

The amount of rusting and the color of the final rusting depended on the humidity in the air around the parts being browned.  I used a 2% solution I made up using a big bag of ammonium chloride crystals (powder).

If you look at some of the "modern" cleaners that claim to kill most common bacteria you see a solution of ammonium chloride being used as a sterilizing agent.

The original source of ammonium chloride was China.  Then later India.

Ammonium chloride is one of a group of chemicals known in chemistry books as "manure salts".   Produced in manure piles.  Really corroded manure spreader parts when I did farm work.

My 2% solution was a bit strong by some standards.  At high humidity it created a lot of crust on the metal and gave a rather dark color brown.  At very high humidity it gave a black non-adherent rusting with a lot of pitting.

E. Ogre