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Steel patinas: blue, brown, black, parkerize, phosphoric
http://www.paranoia-towers.com/armoury/blueing/
"Blueing and metal patination are the processes of putting a decorative or protective finish onto the surface of a metal item. Usually this is steel, especially for protective finishes to prevent rust, but brass and bronze are also decoratively patinated.
In the next week or two, I'll be adding some descriptions of old blueing processes, and my experience of recreating them for the home workshop.
Oil blueing
Hot salt blueing
Cold chemical blues
Parkerizing
Preserving blued finishes
Some rough notes on blueing, thanks to the 'Bat
Introduction
Lots of processes for this, with a range of colours and qualities (in rough order of increasing difficulty).
Heat blueing
Cold phosphoric acid
Hot oils
Cold selenium blues
Nitrate blues
Parkerizing etc.
All blueing processes rely on scrupulous cleaning beforehand and degreasing with acetone. Any oil or grease left behind will ruin the finish, even if it's a small crack with oil that only leaks out when heated.
Don't use the hot processes (oil or salt) on firearms, unless you're sure that the heat won't cause damage. This applies particularly to side-by-side shotguns, with soldered barrels.
Heat Bluing
When tempering steel, colour is commonly judged by watching for the progressively darker "temper colours" to form. One of these is a deep and attractive blue.
This oxide film isn't robust, and so it's not a finish that's useful for gunsmithing. It's popular amongst watchmakers though and is the traditional finish for clock or watch hands protected under a glass crystal. The British Horological Institute has some good notes on bluing clock parts
It's simple to form this blue colour. Clean and polish the item as usual, then heat it. You'll need to watch carefully until the correct colour forms. Once coloured (and cooled) protect with a wax polish, like Renaissance wax. Heating can be done with either a spirit lamp flame, a hot air gun, or heated in a dish of sand. The presence of brass encourages this blue colour, so watchmakers often use a bed of brass filings, rather than sand.
Phosphoric Acid
Cold acid processes are familiar to car-repair and rust prevention. Wipe or dip the piece with concentrated phosphoric acid, to form a nice stable black finish. This works better on slightly rusted steel, so clean and degrease the piece first, then "brown" it to form a thin rust layer by hanging it up somewhere warm and damp for a few days (shower cubicle, airing cupboard, heated "tent" with a dish of water at the base).
Conc. acid is better than diluted (blackens better, causes less corrosion). Cheapest source is from a garden hydroponics supplier (pot growing supplies) ! "Naval jelly" and similar potions are very expensive. Many commercial potions are thickened as jellies, to make them easier to apply. This is just a little methyl cellulose - you can even use wallpaper paste or another starch.
After blackening, wipe with oil or wax to preserve.
Hot Oil
Oils are a matter of heating the piece with a blowtorch, then wiping with an oily cotton rag. Repeat until the colour is adequate, then use a wax polish to finish. Expect the rag to catch fire a few times, so work appropriately. Vegetable oils give browns, mineral oils a blue (nice - I have a steel desk done this way), the best black comes from used engine oil.
Cold Chemical Blues
Cold blues are best bought from shops - look for Birchwood Casy products. They're easy to use, but the selenium is highly poisonous, so wear appropriate protection. Although they give a good looking finish, it's not as rust-resistant as a hot blue.
Follow the instructions on the tin, with two caveats; degreasing must be obsessively clean (wirewool, then a wash with acetone on clean kitchen roll). also the selenium compounds are horribly toxic (gloves, glasses, don't work in the kitchen etc.).
I'm not kidding about selenium toxicity. Mercury inlaying is fine by me, so is asbestos, nitrates, and all sorts of other stuff. Selenium OTOH, is worrying.
Hot Salt Blues
Salt blues give a deeper, glossier finish that's more rust resistant. They should only be used by those who appreciate the chemical and fire hazards inherent in the process. There are several chemical compositions that can be used, but they're all an oxidising salt like saltpetre, used at high temperatures. This is a major fire hazard, comparable to fireworks manufacture ! Some mixtures use caustic soda too, to reduce the melting temperature, at the cost of also being highly corrosive. It may be difficult or illegal to obtain the necessary chemicals in you locality.
Nitrate blues are great fun, but easier on small pieces than large ones. Simply immerse the piece in a bath of molten potassium nitrate (saltpetre) for some 10s of minutes, then admire the beautiful "colour case-hardening" effects. Of course it's not that simple - the Chemist wil be along shortly to explain the full process.
The downside of this is that saltpetre is, of course, a powerful oxidiser. Purchase and posession may be difficult (or even illegal) in your locality. There's also the safety aspects of very hot liquid baths, hot oxidisers, and many others. If you don't degrease carefully, it will catch fire. If the piece is wet, you can get a steam explosion spraying oxidiser around the workplace. Certainly don't try to stir it with a wooden stick.
Another issue is that it's a white powder that's potentially poisonous. Don't leave it on the kitchen table in an unlabelled coffee jar.
That said, "kitchen stove" blueing can be a rewarding process and can give good results, even on your first attempt. Useful tools are a cheap stainless steel stockpot (deep pan) and a stainless steel tea strainer / tea infuser; a wire mesh sphere used to hold small components like screws for blueing. Personally I'd also use a thermocouple thermometer.
Hot blueing is hazardous ! Large pots full of hot oxidisers are not to be trifled with ! If you stir them with a wooden stick, it will catch fire immediately, so imagine what could happen if you spilled it. Don't even think about it without a couple of large CO2 fire extinguishers to hand.
Other Processes
Parkerizing is another interesting process, but these phosphating processes are beyond the home workshop.
A few other texts, sourced from around Usenet.
The following is from "Foxfire 5", pages 334-336:
1 oz. Muriate Tincture of Steel
1 oz. Spirits of Wine
1/4 oz. Muriate of Mercury
1/4 oz. Strong Nitric Acid
1/8 oz. Blue Stone
1 qt. Water
These are mixed well and allowed to stand to amalgamate. After the oil or grease has been removed from the barrels by lime, the mixture is laid on lightly with a sponge every two hours and scratched off with a wire brush every morning until the barrels are dark enough, and then the acid is destroyed by pouring boiling water on the barrels and continuing to rub them until they are nearly cool.
Presumably "muriate tincture of steel" is ferrous chloride (FeCl2), "Spirits of wine" is ethyl alcohol, muriate of mercury", is mercuric chloride also known as corrosive sublimate (HgCl2), and "blue stone" is Copper sulphate.
Another recipe for "Birmingham Imitations" calls for the following:
1 oz. Sweet Nitre
1/2 oz. Tincture of Steel
1/4 oz. Blue Vitriol
6 drops Nitric Acid
14 grains Corrosive Sublimate
1 pt. Water
When the barrels are dark enough, drop a few drops of muratic acid in a basin of water and wash the barrels slightly to brighten the "twists". [This obviously refers to finishing a twist in shotgun barrels, the final acid wash to remove some of the brown finish.
It is important that all grease or oil be removed using lime as mentioned. Dust hydrated lime on a cloth pad and rub vigorously, renewing the lime as necessary. Otherwise, boil the barrel in a weak solution of lye. Do not handle the cleaned barrel in the bare hands as oil from the skin will leave finger marks. When boiling, if you do it that way, put wood plugs in the ends of the bore and hold by the projecting ends.
We found these recipes in For Beginners Only, by B. M. Baxter, published by the National Muzzle Loading Rifle Association.
After sitting overnight, a fine coat of rust would cover the barrel. Give it another coat of solution, being careful not to touch the barrel. In humid weather, the barrel will rust rapidly. Repeat the process for four or five days or until it has a good coat of rust. When it has a good, even rich covering, scald the barrel by holding it under a hot faucet until the barrel is hot. This will neutralize the acid in the browning solution. Then give it a good coat of linseed oil or motor oil while the barrel is still warm.
Hacker Martin explained his blueing and process to Ogilvie H. Davis in the August 1970 issue of Muzzle Blasts:
Gun browner is made by taking a pint of water, a pint of rubbing alcohol or radiator alcohol, mix and throw in a handful of Bluestone along with a teaspoon of nitric acid. Shake the mixture well and set away for a few days. If you want it extra fast, add a quarter of an ounce of Corrosive Sublimate of Mercury. Wet the iron with the solution, then let it set until dry and rub off with steel wool, wet again and repeat until the brown suits you. This may take three days or three weeks.
You can blue the above by boiling the rust off in plain water, then wooling down, continuing until the color is dark enough to suit. No trouble getting this solution to take hold, I wipe the surplus grease off a barrel, and smear it on hard. I scrub the iron, in fact no trouble in getting it to stick. Do not get the mixture on your skin, as too much will cause a burn.
For applying the mix, a piece of rag set in the cleft end of a wooden stick is fine. This can be thrown away when the job is done, as the acid eats up the stick pretty fast.
Heat the armour to a dull red and then quench it in oil. This would give you a matte black finish, tumbling it in nutshells would give a satin black finish. It will also create a case hardening within the armour pieces. It will need to be drawn down probably an oven may work at 400 degrees for 2 hours, then bump it down to 350 degrees for 1/2 hours, 300 degrees for 1/2 hours and turn off oven and allow to cool with out opening the oven door. That should take it to a rockwell 60 or 80, which would take a direct hit with an axe and barely sustain a scratch.
Another method would be to heat the armour to a dull red, then quench rapidly in a salt brine solution. This will also need to be drawn in an oven as above. If it isn't drawn correctly it will be very brittle almost like glass. This one will give a black to charcoal finish of varying shades and hues within the same piece.
Try these recipes out on a small piece first, until you get comfortable with the processes. The last two methods are from what I remember from working in a heat treat shop. Coloring was not a great concern the case hardening was though. "
"Blueing and metal patination are the processes of putting a decorative or protective finish onto the surface of a metal item. Usually this is steel, especially for protective finishes to prevetn rust, but brass and bronze are also decoratively patinated.
These are just some rough notes on oil-blueing. I'll improve and illustrate them when time permits.
Hot Oil
Oils are a matter of heating the piece with a blowtorch, then wiping with an oily cotton rag. Repeat until the colour is adequate, then use a wax polish to finish. Expect the rag to catch fire a few times, so work appropriately. Vegetable oils give browns, mineral oils (including fresh engine oil) a blue (nice - I have a steel desk done this way), the best black comes from used engine oil.
The best torch is quite large and powerful, but relatively cool. An oxy-acetylene welding torch will work, but tends to cause local warping and is slow to work with. Better is an oxy-propane nozzle, especially a wide, flat flame-cleaning nozzle
"
Sealing wax recipes
for cutler's pitch experimenters
http://www.paranoia-towers.com/alchemy/sealingwax.htm
'paint' for rustproofing iron
"Japanning"
http://www.paranoia-towers.com/alchemy/pontypool.htm
Glossary of old chemical names
http://www.paranoia-towers.com/alchemy/glossary.htm
I'm thinking about getting the Pecard's, what do you think, would it make a good substitution? Better perhaps?
