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Old 01-16-2008, 03:44 AM   #71
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I know there were a couple of different ideas suggested for the final oil coating. What did you finally wind up using, and how?

Oh, and definitely, +1 on the sticky-thread!
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Old 01-16-2008, 10:30 AM   #72
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In the end I didn't use any type of heated on oil sealer. It only has a light coat of oil on it.

I may try that cooked on oil seal next time on the Polish build.
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Old 01-16-2008, 02:33 PM   #73
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Default Coating with BLO and Artist oil?

Hello,

On page 3, USGI gunsmith talked about coating the finished product with a 50/50 mix of Artists oil paint and BLO in a milky consistency. Is that the real mix proportions? It seems like thats an awful lot of oil paint. It seems like that would be a gooey paste at 50/50, not milky.

Am I wrong? It sounds like a great coating but I would like to get it right.

Thanks,

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Old 01-16-2008, 03:20 PM   #74
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I think he is talking about a really small amount. Like a tablespoons worth of oil and a small amount of black pigment. Just go for a dark tinted oil mix.
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Old 01-18-2008, 10:45 PM   #75
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Gasp, it's a sticky! I'm honored. Our new friend USGIgunsmith deserves much of the credit for the great information he has shared with us. I now know more about bluing than I ever thought I would.

J2T. I'm not sure about how close a match it would be to a new Romy G. Pretty close I figure. I have 2 as new Romy G's that I got from Bocefus and they appear to be blued.

I'm doing the next couple of builds right now and one is a Polish underfolder converted to a Polish fixed stock and the other is a Hungarian AMMS kit that is like new.

The polish rifle is a compete refinish job like my first one.

The Hungarian rifle kit is like new and in original condition it is BLUED. So what I am doing there is to rust blue the NDS receiver only and see how that matches up to the original finish. I'll know more in a few more days and will post new pictures.

One of the things that I have done differently this time is I used a COARSER blast media. 70 grit this time instead of the 120 grit I used the first time. I'm just now carding the first rust/boil cycle and things are looking really good. Maybe even better than before. I'll know more in a few days. The idea was that the rougher blast media would create an even more matte blue finish that will better blend with the original Hungarian finish. We'll see in a few days.
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Old 01-20-2008, 02:53 PM   #76
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I have a really good freind that uses this method. He goes up in the mountains and collects snow to use instead of tap water. He swears that the impurities in the water can add problems the same as an oily fingerprint will. I'm not that smart, but I can't argue with the finish he gets.... any thoughts on this?
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Old 01-20-2008, 05:55 PM   #77
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The better the water the better.

I used tap water, really bad tap water and things still worked. When I switched to RO water the red turned black more thoroughly. I only use RO water now.
Distilled would probably be better as would snow or rain water.

Use the best water you have around.
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Old 01-20-2008, 06:13 PM   #78
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Use distilled water. It costs $1 per gallon. How much is your gun worth?
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Old 01-21-2008, 04:41 PM   #79
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About the issues some are having in getting the rust to form in an arid climate- why not get one of those room humidifiers from a drug store, and use distilled water in it in a room with the parts hanging in front of it? If THAT doesn't provide enough moisture to rust them, I can't imagine what would.
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Old 01-21-2008, 09:26 PM   #80
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The lack of rust in a desert does make this take a while.

But I have been experimenting.

You can run a hot shower in the bathroom and keep the parts in there...this works better than nothing but you need an extra bathroom and it isn't terribly efficient.

Now this works, run your DISHWASHER on it's shortest cycle, (empty diswasher) and as soon as it finishes its last rinse put your parts on a tray of some type and get them in there. THIS WILL CAUSE RUST and a LOT of RUST in just an hour or so. Be very careful doing this as you can rust too much. It makes rust FAST. Still, probably not real energy efficient.

What I did the last 24 hours is something that was suggested by USGIgunsmith a few pages back.

I took one of the big plastic storage boxes that my wife stores christmas crap in and I took 4 small bowls to use as spacers under the tray of parts. I put a WET towel in the bottom of the box and then set the tray on the little bowl spacers and put the lid on the box. I then set the box where it would get direct sunlight indoors that warmed it up.

I got pretty decent rust in 24 hours. And 24 hours is about as long as you want to let actual rust remain on the parts without boiling.

This is very efficient and looks like the way I'll be doing it for a while.

I tried the humidifier in the bathroom and it did not work as well as the hot shower method.

You don't want to actually get water droplets on the metal so it's not like you can mist it or anything.
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Old 01-23-2008, 10:49 AM   #81
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Just curious, do you have to use the acid to get the metal blue? In the summer down here on the gulf coast you can almost watch the rust form on untreated metal. Humidity is usually over 90%. I wonder if just letting the metal get a light coat of surface rust, boiling and carding would produce the same result?
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Old 01-23-2008, 02:29 PM   #82
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The acid etches the steel evenly over the metal.

According to USGIgunsmith it is possible to use only a saline solution AFTER the first two or three applications of the rust blue solution.

Just letting natural rust form on its own without the acid etching may not produce an even finish.

That is all the rust blue solution really does and is. Acid with some salts in it.

The coloring is all nothing more than red oxide (rust) turned black by heat and water.
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Old 01-23-2008, 09:05 PM   #83
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The credit for this thread goes solely to Val. He had this going well before I chimed in. His observation are right on the money. And based on his excellent results he is clearly a man of talent.

(I tend to keep my experience, thoughts and 'lessons learned' to myself unless predicated by someone's serious involvement or interest.)

The acid slow rust blue solution is needed to etch the steel on the first several applications/cardings. What you are attempting to do initially is evenly grow ferric oxide crystals all over the intended surface of the Steel.

Anyone who ever owned on of those "crystal gardens" in a fish bowl kits as a kid knows that crystals tend to grow better and better in an solution once they have a good start.

After 2 or three rounds of rusting with the acid I have found that a brine solution works better than the acid for the next coats. I also tend to sand lightly with a 800 grit w/d paper at this point during the carding phases to even up the surface. During this phase one is attempting to fill in the surface with additional tiny black ferric oxide crystals and the brine solution causes a fine orange rust. (If an acid is present the acid seems to tend to eat off the rust already formed slightly before new rusting begins.) This brine caused rust boils jet black.


ONE TIP: Areas you do not want to rust can be masked with lacquer paint. I tend to use green lacquer as it is easy to judge when it needs to be repaired. At the end of the process it is also easy to tell when one has removed all of it.
I tend to use the lime green Flocquil railroad colors from the hobby store.

I use soft wood pegs dipped in green paint to seal off muzzle and chamber. I make these pegs by grinding 3/4 inch square pine stock that has been ripped out of larger boards on the table saw into a truncated cone shape on the bench sander. For the chamber peg I shape the peg by eye using cartridge case so it will seat in the chamber only.

I leave the chamber piece long enough to project past the receiver on a bolt action receiver if one is present. These pieces are then used to hold the barreled receiver up off the floor in the rust cabinet. The 3/4 square stocks rests on the support blocks and the entire barrel or receiver is suspended with nothing touching the walls or floor of the chamber.

I drive the peg in the chamber end and then I will spray some "foamy engine brite" spray product into the bore from the muzzle end. The foaming action coats the inside with detergent. I then clean the last several inches of bore with a shop swab dipped in denatured alcohol. I index the second wood peg to the first and drive the second soft wood peg that has been dipped in lacquer in. I tend to cover gas port areas with a small strip of 100 MPH tape that has been cut out with an X-acto knife. I have also at times used rubber tape and metal duct tape. This masking is not always durable and may need to be repaired or replaced in the course of rusting.

After the project is completed the lacquer mask can be removed with 'epoxy and lacquer thinner'.

The lacquer is removed from chamber and muzzle with lac thinner and a chamber brush and shop swabs etc.

I then clean the detergent from the bore using a commercial jewelers steam cleaner because that is what I have in the shop. A tea kettle over the sink works just as well.

I hope this helps.

Quote:
Originally Posted by VALMET_M76
The acid etches the steel evenly over the metal.

....

Just letting natural rust form on its own without the acid etching may not produce an even finish.

That is all the rust blue solution really does and is. Acid with some salts in it.

The coloring is all nothing more than red oxide (rust) turned black by heat and water.
A traditional slow rust blue formula given in the old classic book Gunsmithing by the late Roy A Dunlap. His formula is merely Nitric acid mixed with Sulfuric acid or Hydrochloric acid in a ceramic crock. To this iron fillings are added to saturation. By saturation we mean they are added in an amount to where they will no longer dissolve after several days of sitting. (If one does not have 'iron filings' on hand something like upholstery tacks or steel wool that has been cleaned of oil with acetone can be substituted.)

What happens when one puts this on the parts is that the surface is etched and pure iron will plate out of the solution due to galvanic action and plate onto the surface. I believe the fresh Iron plating is the blue sheen that one sees when one applies the cold rust blue solution for the first time to the bare metal parts. This iron rich surface creates the even rusting.

I start with the acid and then switch over to brine after the third pass.

Last edited by IanMor; 10-05-2013 at 11:09 AM.
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Old 01-26-2008, 10:05 AM   #84
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I plan on doing a FAL receiver this way(G-1). What effect if any will this have on a non-barreled receiver like DSA? My concern are for the threads and HTS pin holes for the lower.

Yes, I know they have been done this before, just not by me.

Thanks
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Old 01-26-2008, 12:14 PM   #85
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Rust blue is a controlled rust process.

You only apply the solution to areas that you want to blue and not to areas you don't want to blue. Plunger holes, pin holes, bolt slots, grooves are all fine and not affected by rust bluing. Threads are safe as well, just don't put any rust blue solution there.

What actually happens with rust blue is that a fine crystaline bloom is created over the surface of the steel. Once that bloom is achieved the parts are boiled and that surface oxidation is converted to the color we are after. Here are a couple of pics that show the beginning of a rust cycle. You can see the rust in it's very early stage as it just begings to bloom. These parts have been rusting only a few hours and are cycle 4 as in four rust and boils have been done.





The rust is never allowed to remain on the steel long enough to cause damage from actual corrosion. The process is stopped by boiling and then restarted.

It is important to never allow the metal to rust for longer than 24 hours. If you live in a warm, humid climate then 12 hours max. You are looking for a finely textured crystaline bloom of rust. Don't worry if all surfaces are not identical in appearance as this is a repititive process and all areas will eventually even out.

The important thing to remember is that you need it to rust evenly over the surace and that is it. Then boil it. If you FORGET or NEGLECT the rusting process and allow it to continue for too long then yes, you can damage your parts by allowing actual corrosive action to begin, as in pitting the steel and having parts rust-freeze in place.

Remember the time limits. You will learn from experience how to guage the degree of rust present.

I rust blue every single AK part except for the firing pin, the firing pin retaining pin and the extractor retaining pin.

I learned something today.

Pay attention because this is important concerning "sealing" your rust blue job with an oil/paint seal coat.

Today I took some lampblack oil paint, some artist grade linseed oil and some thinner and mixed up a very thin mix to coat the rust blue with. After discovering that I can fit a complete barreled action in my oven when set at an angle I figured I'd do the rifle that is the subject of this post.

Well, I applied the oil/paint coat too thick and then baked it on.

Now my beautifiul rifle looks just like a SAR! Ugh.

And, you can't get this stuff back off. So far it has resisted any and all solvents I have around here. So I'm not sure what I am going to do.

What I learned as a proper way to do the seal coat is this. Go ahead and mix up your linseed oil and oil paint. A half teaspoon of oil paint and 2 teaspoons of linseed oil and 2 teaspoons of thinner make enough to "seal" two rifles. Paint the parts giving them a good coating and then let them air dry for an hour or so. Then, use rags or paper towels or whatever to wipe away almost all of the oil/paint mix. There should remain a very light film of linseed oil and paint and that is how much of a seal coat that you want. Bake at 300 for 1 hour.

You wouldn't think that simple oil paint and linseed oil would make such a hard, durable finish so quickly. Believe me....it does.

Last edited by IanMor; 10-05-2013 at 11:09 AM.
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Old 01-26-2008, 11:56 PM   #86
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Well you are very welcome.

I discovered that no gun solvent will remove the oil paint. However, hot water, soap and 0000 steel wool will.

Whew....

So I cleaned of all the original sealcoat and guess what? The rust blue underneath is just as good as ever.

So I am going to redo the barreled action as above. Paint it with the linseed oil/oil paint mix, wipe most of it off, bake it 1 hour at 300.

Once it cools off paint it up with plain mineral oil and bake that for an hour at 200. Then wipe it down good.

There you go, properly sealed and oiled rust blue finish.



Eh, could've wiped it down a little better. Excess oil shows up in the daylight picture.


Last edited by VALMET_M76; 01-27-2008 at 07:34 PM.
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Old 01-28-2008, 05:38 AM   #87
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OOps sorry. Perhaps I did not make it clear.

The finish left by the rust bluing is somewhat absorbent and matte like an Iron oxide film (not unlike a very thin rice paper in thickness and texture) and the idea is to add a tough baked on matrix of pigmented oil to this to add water resistance and durability.

I have seal coated with unpigmented oil and pigmented. In my humble opinion the job comes out better with pigment for the following reasons. 1) when the oil is pigmented one can see that the application is even. When unpigmented oil is applied it is never even and when baked tends to look more uneven. 2) the pigmented oil adds a complementary secondary color to the finish that is common to professional finishes. We are used to finishes having some depth of color. 3) Unpigmented linseed oil bakes with a tan tint this adds a brown "secondary color" tint to the final appearance when the surface is stripped of lubricating oil.

The pigmenting ads depth and consistency and shades the oil inside the iron oxide to match. The pigmented oil tends to even out the color and the pigment keeps the baked oil from scuffing. Also the pigment in midnite Black artist colors is itself black ferric oxide.

The idea here is to have about the lightest coat possible applied and still have it wet.

Seal coat should be as thin as one can possibly make it.

So thin that it is not possible to get fingerprints.

I wipe it on very thin and wait a half and hour or so for it to thicken up (catalytic reaction plus all lighter solvents evaporate).

Before putting parts in the oven to bake I often wipe down with dry paper towels until almost everything possible has been gotten off.

The idea is to seal the iron oxide grain with a pigmented oil. The oil should be "in" the grain of the rust blue surface not "on" it.
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Old 01-30-2008, 12:17 AM   #88
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Quote:
Originally Posted by USGIgunsmith
The oil should be "in" the grain of the rust blue surface not "on" it.

That is absolutely correct, and not quite as easy as it sounds.

Note:. USGIgunsmith is sharing a trade secret with this info, far more signicifacant than you might think.
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Old 01-30-2008, 12:57 AM   #89
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What is the advantage of doing this over hot-bluing? From the sound of it hot-bluing is a LOT easier and more durable. I've been doing hot-bluing for several months now, ad the first rifle I did has been (ab)used a lot, and the finish is still fine. It took about 2 hours to do, and I can re-use the solution indefinitely. It also looks to be a much deeper coloration that rust bluing.

By the way, the first time I blued I wore rubber gloves to prevent fingerprints. Nowadays I hang the rifle by iron wires, so I never have to touch it until I'm finished. It's easier.

Rust bluing looks really interesting and I'd like to try it, but from your descriptions it seems difficult and fragile. Perhaps you overstated these?
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Old 01-31-2008, 01:12 AM   #90
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It isn't fragile. Rub one of your hot blued guns with a stainless brush and steel wool HARD for an hour and see if it looks BETTER or just ruined.

Rust blue is the old world way of bluing firearms. Hot blue is a modern, as in 1936 being modern, shortcut method.

It takes considerably more time but produces a world class, LIFETIME finish that is probably ten times more resistent to rust than is hotblue.

There are also no dangerous, toxic chemicals to deal with other than a small swab of bluing solution and a pot of boiling water. No fancy tanks, no expensive chemicals, no serious heaters......no nothing besides a bottle of solution, some steel wool and some boiling water.......and time. An hour of time every other night for a week can produce a finish that anyone should be proud of.

Hot blue is a method developed for speed in production. It's way less labor intensive and much faster once you've gone through the expense of setting up the system. Important for a production system for a Arms factory or even a gunsmith.

I thought about setting up a hot blue system..

Not anymore.
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Old 01-31-2008, 11:30 AM   #91
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USGIgunsmith, what product do you use when sealing your bluing? You talked about pigmented v unpigmented oil. Where does this product come from? From Valmet_M76's post it sounded like he painted his rifle after bluing it. I don't want a painted rifle - that's why I'm bluing to start with.

Please explain this step to me. Are you just oiling the blued rifle or are you actually applying paint? And why the baking? When I hot-blue I apply oil over the finished product, but only a sprayed-on or hand-rubbed coat.

Last edited by my-rifle; 01-31-2008 at 11:36 AM.
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Old 01-31-2008, 12:14 PM   #92
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The oil paint/linseed oil sealcoat is just a sealer with a slight black tint to it so it is dark and not yellow as it would be with just the linseed oil. Think of it as more of a permanent oil finish, not paint.

The other effect the sealcoat has is it BLENDS everything together nicely.

On my first attempt at sealing I did not do it correctly and removed it and then did it right. The correct method is already explained two times in previous posts.

I am in the process of finishing two more AK builds that are rust blued. One is a total refinish and the other is just a receiver rust blue that I will match to a excellent condition Hungarian kit.

The sealcoat technique looks like it will provide the final blending effect matching the receiver to the kit finish.
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Old 02-01-2008, 01:49 AM   #93
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Again USGIgunsmith, what is the product you're calling pigmented oil? Also I'm still curious about what the baking does. Does this form the oil into a lacquer-like finish? Are we making a clear-coat here? I'm still wondering why it's necessary to bake it. What for example, would happen if you just oiled the blued rifle instead of baking it?

OK, another question regarding this method: How do you blue an assembled rifle? I mean if you have to paint on the bluing agent, then card off the rust with a brush, how do you get under the front trunnion? Inside the rear sight block? Inside the front sight block? Is there a more, do-able way of doing this, or can it only be done before the rifle is assembled??

Last edited by IanMor; 10-05-2013 at 11:12 AM.
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Old 02-01-2008, 09:24 PM   #94
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The advantages of slow rust blue over German hot blue:

1) Control - The process is done in several stages and gunsmith can tweak the process by selective application of acids or brine with a q-tip. ---- In the German hot Blue process the parts are concealed from view and a problem will be unknown until parts are removed from bath. In hot blue very often results are less than good and gunsmith must strip and start over.

2) Durability - In slow rust bluing the parts are burnished as the bluing progresses. Slow rust bluing is two to three times more durable than hot German blue. This produces finish that is more uniform in thickness. Crystals in the finish are more uniform in size. Slow rust bluing produces uniformly small crystals as the crystals are grown slowly. ---- In hot German bluing crystals in the middle of say a Mauser 98 receiver ring or a Ak-47 receiver side may be larger and thicker based on the temp of the bath and solution strength, but towards the edge crystals will be smaller and the finish will be thinner. This means the finish may be thinnest where it is needed most.

3) Beauty - Slow rust bluing can be used on Milsurp guns or fine custom guns. The thickness of the blue can be controlled and a classic gray finish can be achieved if desired.
Slow rust bluing is the only way to control depth and color of bluing.

4) Simplicity - Slow rust bluing consumes a few pennies of materials and a few minutes of labor each day.

5) Versatility - Slow rust blue process can be used to produce a variety of finished appearances. The finish on a German guild rifle can be restored or duplicated by burnishing more and burnishing with a stiffer brush and halting the process at the dark gray gunmetal color. Slow rust blue can be used to duplicate the German hot blue finish by burnishing and carding with a NYLON tooth brush. The final finish will be blacker, thicker and more opaque.

6) Double guns - On fine double rifles and shotguns slow rust bluing is the only process that can be used. Any other process will desolder the silver soldered barrels and cause the solder to Galvanically plate out all over the barrels.

Pigmented oil?

I use artist grade boiled Linseed oil. Artist grade is different than regular boiled linseed (home stores) in that it is ultra-refined and made using an alkali process that makes it non-photo reactive. Fine art oil paintings are now made to last for hundreds of years because of the higher grade of materials that have been developed since the old masters.

This is base oil mixed with artist grade lamp black or midnite black 50/50. Lamp black is a tint that is slightly more gray and I believe it is made in the modern era by burning cork scraps left over from making wine corks. Back when artists made their own they often used soot from oil lamp (hence the name) or burned cork from a wine bottle. Midnite Black is made from black iron oxide. This was traditionally made by putting scrap iron or nails in a crock to rust and then boiling the loose precipitate to turn it black. In the modern age I believe they simply grind/conch an iron oxide ore found in the ground.

Grumbacher and Windsor & Newton are two brands of artist grade blo and pigments. Grumbacher is from USA and not conched as fine. It is more economical and used for larger paintings more likely to be seen from a distance. Windsor & Newton is from the UK and conched very fine. Windsor & Newton is considered the highest quality and is generally the only paint considered for things like miniature oil paintings. W &N now has a more economical brand out to compete with Grumbacher. The two brands are sold at artist supply stores. Sometimes I mix the pigment heavier in proportion to the oil sometimes thinner. Sometimes I add MEK to thin out the mix. It is all based on the finish that has grown on the metal and the end finish desired.

I generally wait about an hour before baking. This gives time for volatiles to escape and the initial drying and catalytic reaction to start.

I then baked at 350 degrees F for one hour.

Two very thin applications is superior to one. Remember the overall process is forgiving and adding more is easy.

(Please also be aware that both Windsor and Newton and Grumbacher now sell "water soluble oil paints" in tubes. These are intended for hobby painters or art students to learn with and these are not real oil paints. These are an emulsion of oil paint and alkyd acrylic water base tint. These are NOT the ones that we are talking about and these will NOT WORK in this application.)

Last edited by USGIgunsmith; 02-01-2008 at 09:40 PM.
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Old 02-02-2008, 02:02 AM   #95
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Think of the seal coat as a see through coat of baked on oil paint. I found that what worked for me was to dilute the oil base lampblack paint with the artist grade linseed oil until the mix is very thin. Then paint all of the metal and let it dry for at least two hours. Then I took an old tee shirt and wiped away as much of the oil/paint off the steel as I could. Once I did that there still remained a dark, oily sheen to the metal. Once you bake that it is fixed to the steel. Without baking you basically have oily black paint on the rifle that won't ever dry. Once it's baked I then painted the rifle with pure clear mineral oil and let that sit a while and then baked that at 200 for about a half hour and then I wiped away the excess oil. In the end what you end up with is a sealed and oiled blue finish.

I said this once before. This entire process is not unlike seasoning cast iron cookware. If you are familiar with the big black iron skillets and dutch ovens then you know that the finish we are talking about is far more durable than any hot blue.
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Old 02-02-2008, 02:31 AM   #96
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So what would happen to the rust-blued rifle if you just oiled it instead of painting it with a clear-coat?

Again, is there a way to use this process on a rifle that has already been assembled?
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Old 02-02-2008, 10:43 AM   #97
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The clear coat is oil.

I thought it was a strange suggestion when USGIgunsmith first mentioned it until I remembered a custom muzzle loader I once had that was also sealed with linseed oil over the rust brown finish. It really is a neat finish.

Yeah, you can completely omit the step if you want to and just oil up the rifle with whatever you want.

You can rust blue an assembled rifle. It will be more difficult to card the the areas around the turnions inside the receiver and you will need a larger pan for the boiling. As far as difficult carding inside the receiver goes, you don't have to do that perfectly as those areas are not part of the appearance package. As in they aren't normally visible.

As a note, Lugers that are rust blued have internals that are in the WHITE without any finish other than a high polish.
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Old 02-03-2008, 12:09 AM   #98
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This is a rifle I am working on right now. For these pictures you are looking at a riveted up receiver that has been rust blued. All other parts are original Hungarian finish. As you can see, there is a slight difference at this point. Currently the receiver subassembly is rusting, all other parts are as original. We will see whether or not these parts can be blended with a seal coat.









I am also working on a Polish rifle that is a full refinish using the rust blue process. Pictures of that later on.
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Old 02-03-2008, 01:02 AM   #99
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The seasoning of cast iron is a good analogy.

Baking in the oil finish makes it about ten times harder and ten times more durable. "Bulletproof". Baking in the oil combines the durability of a baked enamel finish and the durability of a slow rust blue resulting in a final finish that is several times tougher than either.

A good analogy is high pressure laminate. It is made from paper and plastic. High pressure laminate is tougher than either.

Many similar examples exist in our modern science of materials technology. Fiberglas- fiberglas is a laminate of glass fiber and polyester resin. Fiberglas is stronger and tougher than either alone. Reinforced concrete is stronger than steel or concrete or crushed rocks. Asphalt- it is stronger than crushed limestone or tar alone. A laminated recurve bow limb is stronger than the high pressure laminate backing or the wood core. A carbon fiber laminate is stronger then carbon fiber or epoxy resin. Micarta is stronger than fabric or resin alone. Plywood is stronger than wood. Various metal alloys are stronger than the components alone. Brass is tougher than Copper or Zinc. Bronze is tougher than Copper or Tin. Cupro-Nickel alloy is so tough that the turbine wheels that hold jet engine blades are made from it. As are the frames of rolling mills. Steel is stronger than iron, carbon or oxygen alone. Laminated steel is stronger than steel. Vanadium steel makes better cutting tools. Stainless steel is more corrosion resistant. Aircraft Aluminum alloy is tougher than Aluminum alone. There are hundreds of more examples in modern materials technology.

If one just coats the slow rust blue with boiled linseed oil or heavy mineral oil and does not bake then the final finish is much, much softer and many, many times more prone to scratches or wear. In fact unbaked oil will tend to soften and dissolve the slow rust blue over time. Oil unsticks rusted joints right? Don't we put oil on rusted needle-nose pliers to weaken the bond of the rust to the metal and get the pliers working freely again?

Now put some oil on the rusted pliers. Do not loosen the joint but instead place the pliers in the oven and bake it for an hour and a half. Congratulations- the pliers are now glued together as firmly as if they were WELDED or SILVER SOLDERED.

When you bake in the oil that is what you are doing making a permanently bonded finish that is several times stronger than either component alone.

Isn't that what we are trying to do when we place a corrosion resistant finish on metal? Aren't we trying to deposit a strong attractive finish that is permanently bonded to the surface?

Baking in the oil does just that cement a permanent bond beteen the sealer and the finish. The slow rust blue alone is porous and corrosion may continue if the surface is not sealed with oil. If the oil is not baked it remains soft. Bake in the oil and one has produced a tough durable combination stronger and tougher than either half alone.

And for the record this is not a "trade secret" it has been published in numerous gunsmithing books. Oil has always been baked into the finish of US martial arms (finishes such as Browning, Slow rust bluing, Parkerizing baking in oil was the final step of manufacture). Oil has also been baked into the finishes of most foreign martial arms such as the Oberndorf g98 and k98k Mauser's traditional German hot blue. Oil was similarly baked into the parkerized finishes of UZis, FALs and L1A1s, Aprkerized AKMs and the Parkerized Parts of M-16s and M-4 Carbines. Baking in oil as the final step is the standard last step in the process.

As far as I know the only time Baking in the oil was omitted was in the final stages of WWII. The office of war production of the War Department identified it as a bottleneck and directed baking to be replaced with dipping and drying in early 1944. Similarly late K98s and K-43s and MP-44s with the Parkerized finish have a softer finish indicating the parts were dipped and probably not baked. Some of the guns have a paint on top that chips indicating that the paint was probably not baked.

Baking on finishes to this day is a standard industrial practice. Painted finishes are baked. Parkerized finishes are sealed and baked. Anodized finishes are sealed with synthetic lacquer and baked. Brushed Stainless Steel and Aluminum parts are sealed with synthetic lacquer and baked. Watch "How It's Made" Metal finishes and coatings on everything from toasters to bottlecaps to metal housings of electronics products to the paint on cars are baked. Even big things like jetliners they paint and then lower a hundreds of heat lamps next to the skin to bake it on. Baking is generally the rule- not the exception.
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Old 02-03-2008, 01:23 AM   #100
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I think that some original AK finishes are in fact, blued and baked oil sealed finishes that are mistakenly identified as parked and painted. Those Hungarian parts in the pictures in the above posting are BLUED and SEALED as originally done at the factory.
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Old 02-03-2008, 09:13 AM   #101
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This is a good idea. I think I'm going to try to bake an oil finish on my hot-blued rifles. The hot blue is already tough as heck, but with the baked-on finish it should be even tougher. I like that.
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Old 02-03-2008, 04:08 PM   #102
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German hot blue is tough as heck. It is a great process for industrial scale production. It was used for many decades to produce billions and billions of items. Many of which are still in use. It was used for everything from steam engine parts to firearms to piston engine parts to suspension and steering components.

Other industrial bluing processes were used in that era- like various cyanide processes and another called hot Nitre bluing etc. The cyanide processes had metalurgical advantages but could only be used in industrial setting with highly trained workers and very specialized equipment to protect those workers.

For the home hobbyist doing BIYs and prototype maker doing one offs- the slow rust blue process has several advantages.
If the German hot blue is "tough" the slow rust blue can only be rated as "super-tough". If the German hot blue is "attractive" the slow rust blue can only be rated as "super-attractive". If hot bluing is "foolproof" the slow rust bluing is "super-foolproof". The slow rust blue process has always been an artisan finish rather than an industrial finish.
It takes longer and requires trained and skilled workers. The slow rust blue process actually pre-dates the industrial era.

German hot blue is cheap and effective. If that is one's finish of choice and one is set up with baths and tanks to do it there really is no valid argument to doing the slow rust blue instead on an AK type rifle.

In the industrial era of the Second half of the 19th century and first half of the 20th German hot blue predominated. It is quicker and cheaper. It can be easily automated using chain drive hanging racks to dip thousands of parts into several baths in succession without human involvement etc.

Starting in 1939 the caustic blacking process (like Dulite) has slowly replaced it. Winchester was one of the first US firms to start using Dulite in 1939.

http://du-lite.com

According to their web site Du-Lite provides blacking chemicals to 70% of the American Firearms industry today.

German hot blue is sometimes referred to as "caustic bluing" in old books. Even so not to be confused with modern caustic blacking like DuLite that has replaced it as an industrial process. Blacking finishes are often referred to today somewhat inaccurately as "caustic bluing" and this is a terminology carryover from when the actual process being used really was German hot blue "caustic bluing".

I think Valmet_76 is accurate in his posts that many 1950 and 1960s era AK-47 /AKM finishes that are probably really the German hot blue have been misidentified as Parkerizing.

I think the reality is that some external AKM parts were Parkerized for corrosion resistance. Some external parts were German hot blued. Some internal parts were Parkerized and some were German Hot blued. Perhaps some were blackened using the Com-bloc equivalent of Du-Lite. I think all the parts were then more or less finished to match using a pigmented oil that was baked on.

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Old 02-04-2008, 01:00 AM   #103
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If I remember correctly, Winchester was one of the first in the US to use the Dulite process, to address a problem in the field with the conventional methods of the day. The M1 Garand has a gas cylinder that is made of stainless, and the standard finishes would rapidly wear off and leave this part shiny. Unfortunantly, as it is slung and carried, this leaves a nice bright reflector marking the top of each GI carrying one. So Dulite was used by Winchester to address this problem that Springfield Armory had.
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Old 02-04-2008, 03:03 PM   #104
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Quote:
Originally Posted by Pvt.Joker
If I remember correctly, Winchester was one of the first in the US to use the Dulite process, to address a problem in the field with the conventional methods of the day. The M1 Garand has a gas cylinder that is made of stainless, and the standard finishes would rapidly wear off and leave this part shiny. Unfortunantly, as it is slung and carried, this leaves a nice bright reflector marking the top of each GI carrying one. So Dulite was used by Winchester to address this problem that Springfield Armory had.
Yes, Winchester was one of the first firms to employ Du-Lite. If my memory serves John Olin (CEO of Olin which was corporate holder of Winchester Repeating Arms in the 1930s) had a hand in developing Du-Lite. Du-Lite is a Connecticut based company.

The Garand gas cylinder was the first application of Stainless Steel in a martial arm. The Garand gas cylinder is a forged and machined part. Springfield Armory addressed the problem of blackening by applying a painted and baked on finish. SA had some problems understanding that the surface of a forging that was not properly prepared would not hold a baked on finish properly.


Winchester experimented with various processes for blackening the gas cylinder. We have early WRA gas cylinders that are Iron plated or Copper plated. WRA apparently tried Iron and Copper. Iron plating unfortunately was not a good method as it defeated the reason for making the cylinders from Stainless Steel in the first place! (What were they thinking? Were they trying to "get over"?) I do believe the Iron plated cylinders were Du-Lited by WRA as were other small parts that Ordnance specifications did not call for finishing by Parkerizing. I do believe the War Department came down on WRA for the Iron plated and Du-Lited cylinders. They are rare. WRA apparently then turned to Copper. The Copper plated cylinders were blackened with Liver of Sulfur. The Copper plating was a good solution, but I believe WRA abandoned it when the Office of War Production directed that two coats of baked on black paint would be the only Garand Gas Cylinder finish employed (Nitric acid was a strategic material needed for electronics production and the Office of War Production directed non-electronics industries to convert to processes that did not involve Nitric Acid as much as possible.)

I think the war department put an end to Du-Lite as a military finish fairly quickly. Du-Lited WRA parts are fairly rare. Du-Lite (aka "Steelkote") really is not durable enough for milspec. Other blackeners like Oxynate #7 from Brownells do meet a milspec standard- specifically C13924.

When I used the term "Du-Lite type" to refer to modern blackening chemicals in my previous post I probably should have made a distinction between Oxynate #7 and its predecessors which are milspec and the more common Du-Lite "Steelkote" which is not milspec.

Scott Duff covers more about Garands in his books. If you are interested he was a web site and sells them directly.

In the 1950s SA began to give the cylinders a Zinc Dichromate finish. The Zinc Dichromate is a nice dark finish that is fairly durable. The Zinc Dichromate was also plated on serviceable WWII era cylinders that were to be reused. The process involves plating on a zinc coating and then chemically blackening and dying like an anodised finish. Zinc Dichromate is the common contemporary black finish used on things like drywall screws and socket head cap screws.

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Old 02-06-2008, 03:26 AM   #105
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Valmet or USGI, can the rust blue process be temporarily halted; say before the next rusting step, and then started again? The reason I ask is due to the fact that I'm out of town for 2 or 3 days at work. I would love to try this method if it can be done with my schedule.
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