Fume Bluing

[dimeN]

ah thank you sean69

that is quite and interesting read ! I have no experience with fuming the acid but i've alot of experience with using diluted acids for etching steels. The mix of acid hcl and nitric is aqua regia, and definitely the vapour would produce a flash rust on steel/iron ( cept stainless steel which the added chromium in the steel makes it much much more corrosion resistant )
-etching ultra high carbon steels in a solution, i can get dilute nitric to give the steel a blueish to deep blue color.. but not so much for iron/lower carbon steels (which is out of my field ) so i do know that the nitric is capable of giving the steel a blue color

if i may recommend something... go with a glass tank ! make a long aquarium type tank and seal the seams with silicone ... i would not make the tank too much bigger than is necessary ( otherwise you'll just be wasting acid and rusting everything else in the room if it vents ! ) use a store bought dehumidifier to control the humidity in room. I would control the air temp of tank ( temp generally has a big affect on speed of chem reactions )
- also, etching colors will change depending on the alloy ( so your test samples to calibrate ..should be very similar in alloy to the barrels you intend to blue )

nb.. you will have to give thought to how to degrease the barrels ! I can tell you that any grease,film, or finger print can potentially confound the process ( this is my experience with putting steels in dilute acid solutions )

its too bad i don't live in your area, i would have liked to have helped out ! this is a great experiment

not sure on your background, but i do recommend brushing up on acid safety ( reagent grade stuff is serious biz )

 

[sean69]

ah thank you sean69

that is quite and interesting read ! I have no experience with fuming the acid but i've alot of experience with using diluted acids for etching steels. The mix of acid hcl and nitric is aqua regia, and definitely the vapour would produce a flash rust on steel/iron ( cept stainless steel which the added chromium in the steel makes it much much more corrosion resistant )
-etching ultra high carbon steels in a solution, i can get dilute nitric to give the steel a blueish to deep blue color.. but not so much for iron/lower carbon steels (which is out of my field ) so i do know that the nitric is capable of giving the steel a blue color

Interesting comment on the mix of acids, any comments on the proportions?
To clarify, you are using diluted (distilled water?) Nitric acid directly on your work? no other chemicals/acids etc?

if i may recommend something... go with a glass tank ! make a long aquarium type tank and seal the seams with silicone ... i would not make the tank too much bigger than is necessary ( otherwise you'll just be wasting acid and rusting everything else in the room if it vents ! ) use a store bought dehumidifier to control the humidity in room. I would control the air temp of tank ( temp generally has a big affect on speed of chem reactions )
- also, etching colors will change depending on the alloy ( so your test samples to calibrate ..should be very similar in alloy to the barrels you intend to blue )

nb.. you will have to give thought to how to degrease the barrels ! I can tell you that any grease,film, or finger print can potentially confound the process ( this is my experience with putting steels in dilute acid solutions )

Been giving it some thought, I had been reading that some plastics won't react readily to the fumes form different acids, (still to be more thoroughly researched) so I was considering a clear polycarbonate/ABS/PVC/polyurethane tube with some type of method to isolate the acid mixture to prevent splash/spillage and some type of venturi valve to evacuate the fumes through a water/carbon filter (assuming that would work.) The thought being that if we have to decrease the density of the fumes for each cycle, it can be controlled more accurately by using less or more dilute acid mixture each tie rather than 'guessing' how much fumes may be in the box! [I really hate guessing - my background is engineering ]

Aquarium glass would certainly be cheaper, though more likely to get smashed by a swinging barrel

its too bad i don't live in your area, i would have liked to have helped out ! this is a great experiment

not sure on your background, but i do recommend brushing up on acid safety ( reagent grade stuff is serious biz )

No kidding!! my biggest concern is controlling and/or neutralizing the fumes, protective clothing & gear is very specific, princess auto crap is not to be trusted!
That and having disaster recovery solutions close at hand and ready (neutralizing solutions, eye wash bottles, a phone dialed 9-1- etc... )
Speaking of fumes, I have not read anything yet that recommends any sort of respirator/lung protection, it's always "fume hood"

 

[dimeN]

my application of dilute acids are on pieces of ultrahigh carbon steel in a quenched/hardened state (tempered martensite or fine pearlite ) .. they react differently etching in a solution than a sample of iron or low carbon steel ! The quenched uhcs will generally take on a blue to deep blueish color . A low alloy carbon steel when etched in the same solution will take on a grey to lite grey-ish with a hint of blue, or orange/brown if solution is off. Yes, i do use distilled water and sometimes filtered tap water.
- i know that this kind of etch would not work for barrels as the alloy used in the metal is low carbon.
- i'll also go through an additional step after to neutralize any of the remaining acid on the metal piece, otherwise oxidation can pop up . ( and immediately apply a barrier oil after whole process is done to maintain finish )

I can tell you that the handy thing about using glass is that you can actually see the process, real time ! Depending on the alloy, you can have much different rates of etching. ( for example, if you have a tad of phosphorus in the steel.. it does dramatically resist the effects of acid... you can see this effect in the twist cores of viking swords, alternating layers of low phosphorus steel and higher are used to create patterns/ also alot of old wrought iron used in the shipping industry tended to have more P alloy to resist the salt corrosion.
- so if it were me, i'd like to see the process with eyes ... as potentially if you over etch the steel, it may start pitting/ over rusting the sample ? or you may end up with color variations that are not as pleasing ?

venting: your dealing with very small amounts of acid, so if you were doing it in a garage with the door open, i wouldn't expect a problem (put a fan at back of garage to push airflow out). ... but indoor, i'm not sure ( a sheet metal hood and perhaps a bathroom fan with some ducting out the window would work ... an inline fan might not last as long as you like but they are cheep lol )

i did use these chemicals when i was in university and continued all along ( had training in safety ) that being said i'll use acid resistant gloves safety glasses, long sleeve shirt, face shield, glass flasks labware but then again you aren't diluting acids (add acid to water, never water to acid = boiling splashing danger)

the concentrated fume can be dangerous, just keep your face back and away from the liquid acid ... breathe it in directly and i imagine it would easily scorch your lungs ( if it was diluted down to the strength of vinegar, it wouldn't be nasty at all...its this reagent grade that demands respect ! ) I would start your experiments out in open air.. then you could see if the process is actually worth its salt without investing alot into fume hoods etc

the mix: in this case you'll have to experiment ! I try my best to avoid making fumes and in this experiment you are trying your best to make fumes lol I'm very excited to see your outcome and the effect it has on the steel samples ... theres nothing like an experiment to replicate an old technique, its very interesting !!!

another problem: what do they mean by carding ? if you abrade the surface too much, you'll lose the patina ! so you'll need a method to reduce the Fuzz, but leave enough of the finish ( could be a problem if finish is shallow )