Gun finishing questions

May 30, 2004 07:09

i cann't answer all your questions but can help with some. modern blueing used a caustic solution of salts heated to -+385 deg. f. producing a deep dark finish. case hardened parts can be blued but might not come out the same color as other parts. worn case hardened parts can be recased.

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CountryGunsmith

May 30, 2004 08:48

OK, here goes.

Modern, or "hot bluing" became popular after World War II. It uses a supersaturated solution of caustic salts in water heated to about 290 deg F (much over 300 deg and the parts turn a brick red). That temperature varies with the salt preparation and the metal being blued. The two most popular salts commercially available today (Brownells' Oxynate #7 and Dulite) both run a touch under 300 deg. I have had to heat up to 310 deg to get good color on some really hardened parts such as older S&W cylinders. This is the standard method used today, gives a deep black finish with luster dependant upon the amount of metal preparation.

Charcoal and Nitre-Bluing are similar but different processes. Charcoal bluing relies on heat to color the steel, while Nitre-Bluing uses molten salts (no water) to accomplish much the same thing. Colors from a light straw yellow to a rich peacock blue to a deep blue/black can be obtained with practice.

The most common type of metal finishing prior to modern hot-bluing was rust-bluing. This involves swabbing the metal with an oxidizing agent, allowing it to rust for a given length of time, then boiling the parts in water to convert the rust to black oxide. A very time-consuming, labor-intensive process that results in a very deep, blue, rich finish. To me, the best blue possible is a good rust blue.

Case-hardening is a process where the part is packed in a bone-and-charcoal mixture then heated in a furnace to well over 1000 deg F. The part is then quenched in water creating a carbuerized (or case-hardened) skin on the surface of the metal. The colors are created by the mixture of charcoal and bone. In order to get a good blue on a surface that has previously been case-hardened, it is necessary to polish the 'skin' away; otherwise you will get an uneven, splotchy blue. The problem there is that most of the frames, etc, that were case-hardened are not of suitable steel for hot-bluing, so they come of the tanks a plum color. They can be re-casecolored. Do not confuse Stevens 311 or H&R Topper receivers with case-hardening. That was a faux casehardening using a cyanide process that is no longer in use today.

Older guns like Winchester lever actions had several different metal finish techniques. Rust-blue barrels, case-hardened receivers, charcoal blued screws and so forth. A good gunsmith specializing in restoration will make sure the proper technique is used on the proper parts. Nothing worse than seeing an old nickel-steel Model 12 with a hot-blue finish.

Scrappy Doo sleeps with the fishes.

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nononsense

May 30, 2004 16:44

A good reference for older formulations and historical import, I use this text:

Modern Gunsmithing by George V. Howe

And:

FIREARM BLUEING AND BROWNING by R. H. Angier

Here is another bit of explanation for you to consider:

Types Of Finishes

On this page I'll give some examples of the particular finishes available, and why they are sometimes used on one gun and not another. Or even more important, where and when to use one finish on a gun part and not on another part of the same gun. As an example; a Winchester 1892 made very early on in production had 4 different types of finishes on the same gun. Barrels and magazine tubes were all rust blued, while the loading gates and extractors were fire blued, with the receiver, forend cap, bolt, and screws being charcoal blued (or Carbonia, depending on year of production). The hammers, buttplates, and levers were case colored. Now that's a lot of different finishes all on one gun. But a combination that makes for a very handsome looking rifle. A little later on into production Winchester stopped fire blueing the extractor and loading gate, and just charcoal blued everything with the exception of the barrel and magazine tube remaining rust blued. If you want a custom finish on your gun some of these slight variances and changes to finishes are insignificant. But, if we are restoring an antique gun exactly as it was done when new, one can see why the differences need to be appreciated. This knowledge is not obtainable to one by reading it in a book. I enjoy a continuing study of these guns and their finishes, polishing lines and direction of the polishing lines, how different parts were finished and when certain pieces were finished one way, and then changed later on to a different finish as in our above example, all in an effort to increase accuracy in preserving these historic arms. Lugers are another prime example, as they have been rust blued, hot blued, nitre blue straw colored on their respective parts, and military guns differ from the commercial models. And we have the same scenario with Colt SAA's. Early production revolvers had case colored frames and hammers, with the remaining parts being blued. Then Colt changed their steel, and introduced alloys into their manufacturing process around the turn of the century, which dictated a different process of blueing the barrels, backstraps, trigger guards, and cylinders. Another slight change is the late production guns having hammers blued with bright sides instead of the typical case color. Again, all these slight variances are very important when accurately restoring a fine antique firearm. Now, on to the finishes.

Bone Charcoal Case Color: Case coloring as it pertains to firearms finishes, is used mostly as a finish for appearance rather than to introduce into the steel a great depth of hardness. That's not to say that the hardening imparted into the steel is not intended for it's mechanical strength it gives the steel, but that we strive firstly for the pretty colors. And that's what everybody loves about case coloring. Simply, case coloring is packing your parts into a crucible along with a mixture of charcoal, bone and maybe a few other "secret" ingredients, heating to a set temperature, holding at the desired temperature for a certain amount of time, and then quenching the packed parts into water. Sounds simple in theory, and it is to a point. Everyone has their own methods and techniques on how to accomplish the desired colors, and types of colors used for different guns. The colors on a Parker double gun for example should not have the same appearance as the colors on a Colt, or Winchester. There are differences between the two. This is one area of gun metal coloration that has a very "artsy" quality about it. If the individual knows his craft well, he will be able to manipulate and control the colors that he gets on his work. I personally tend to like rich and warm colors, rather than the basic blue & gray. But hey, if that's what you like, we can accommodate that.

Carbonia Blue/Charcoal Blue: Another name for this type of finish is "machine blueing" because of the process in which the coloration is applied to the steel. Let me state right here that my method of this type of finish is exactly the same as it was done by the manufacturers like Colt, Winchester, Smith & Wesson, and almost all other arms makers before WW II. By 1939 the hot salt method of blueing dominated arms manufacture and did away with the Carbonia finish. In my opinion, the Carbonia process is the most beautiful finish. It is glossy black in appearance which has a depth to it, that is like a mirror (when the metal is polished to a high luster). Most all Arms manufacturers used this method of blueing prior to WWII. Some of the best examples of this finish, and just how highly skilled the polishers were at that time, can be seen by looking at early 1900's Colt's. To be more specific, if you can examine an Officers model DA, that has something like around at least 90% of it's original finish, you will see exactly what I mean. There are some different methods out there that other shops may use and say it's the correct finish, but to duplicate the factory finish you have to do it exactly like the factories did prior to WW II. This was, and still is for me, a gas furnace operation. Around the turn of the century, many of the arms manufacturers were using different forms of nitrate solutions for their gun metal finishes. The demand for a more efficient output of production brings along the Carbonia method. The trade name for this finish was Carbonia Blueing, and was developed in the United States by The American Gas Furnace Co. in what I believe to be around the year 1905. This finish was used on almost everything steel prior to WW II, like screws and hardware, tools, and arms. You name it, if it was steel and black at that time, it was more than likely blued using this method. At the time it was the most efficient manor in which to blue large amounts of steel. Carbonia derives it's name from the oil mixture that is used to produce this color, which is of course called "Carbonia oil". Once the parts are final polished and meticulously cleaned, they are not touched by a human hand until after the bluing process. At the time the correct color is obtained on the parts, they are removed from the furnace and quenched in an oil solution. This is the most costly and time consuming finish to produce, the care of polishing and metal preparation generally exceeds that of all other finishes. The end result though, is a finish that is just as beautiful, and hard wearing as the factories had produced over 60 years earlier.

Nitre Blueing: Coloring steel with an open heat source is the oldest method of obtaining a blue finish to steel. The Nitre method differs in that it involves an immersion of the part into a nitre bath, which secures a more lasting and evenly colored finish, than by using an open heat source. This is how those beautiful fire blued screws and pins on guns are obtained. As with all forms of heat blueing, the final finish to the metal is vital to achieve the best of results. Any imperfection in the surfaces of the parts to be blued will readily show up when the steel is colored. All the parts are given a mirror like finish and cleaned right before the blueing process to avoid any oxidation on the steel. This is the oldest method of blueing metal that is still widely used for gun finishes.

Slow Rust Blue & Browning: This process (other than heat blueing), is the oldest form of coloring steel. As an interesting note to this finish, it was always properly termed "browning", whether or not the finish was converted to black. There are many recipe's for browning solutions that have been recorded through the years, and for the most part any good one will provide good results when the standard techniques for this type of finish are adhered to. Cleanliness, cleanliness, cleanliness. That pretty much sums up rust blueing. Think about this; a typical gun shop works on guns which are oily and dirty, they are taken down, repaired and cleaned, blown out with compressed air and tested. My point is this, the blueing area is kept separate from the rest of the day to day work area. Any oil spot on a gun will mess up an otherwise perfect job on a rust blue. When you have hours in the polishing and metal preparation, only to have a small little white spot of imperfection on a set of double barrels can be a very frustrating experience. There are some variations of this process that take less time, such as the "Express browns", but the old tried and true method of "slow rust blue" is the only one that I use. This finish is truly into the steel, and is the most durable finish. It's common to see 70+ year old Winchester rifles with barrels retaining almost all of their factory finish. A common thought of many is the belief that this finish is a dull, and flat black. It is true that a crummy, or inferior rust blue job will exhibit a nasty looking flat back. A proper Slow Rust Blued finish should, and does exhibit a beautiful deep shine!

http://www.ronsgunshop.com/finishes.html
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This section has some nice photos to go along with the text. Detailed information is lacking since he obviously wants to sell his services and not educate the masses:

http://www.ronsgunshop.com/carbonia.html
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I hope this in addition to the above gets you on the road to your needs.

Best.

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freemant

May 31, 2004 06:18

Thanks guys!!! I'm going out right now to get a copy of these books. Great info!!!!

Terry

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