Rust Bluing with acid - not having much success

H Wally

H Wally

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Ok, I just lost the original post I was going to put up, so this is the short version.

1) I have prepared 5 test pieces of thin spring steel and tool steel. All have been polished, degreased and suspended from degreased wire.

2)Two have been painted with Hydrochloric/muriatic acid, and the others left bare.

3)A dish of HCL and a dish of water were placed underneath the test pieces in their container. The container was covered and left in the sun all day.


So far it's 12 hours and absolutely no rust on any pieces. A light film of off colour liquid on the two that were painted with HCL, that's it.

I know that most formulas call for nitric acid, but I can't find any. Also, some formulas call for iron to be dissolved into the acid, but since half do and half don't, I figure it isn't mandatory. Perhaps covering the container limited the oxygen available to cause corrosion? If the process used a lot of oxygen it might be a solution, but I don't know.



Anyone have any ideas what's going on? These pieces rusted faster when I left them wet in the shop yesterday. Where to find nitric acid?
 
Try 2 parts water to 1 part muriatic in a jar (don't need much) and suspend the parts from the lid. I've had good results and have found that I can rust twice per day. Usually takes 5 or 6 cycles. A plastic peanut butter jar works well. Heat up mechanics wire to melt holes in the lid and use the wire for hanging. If you have a problem with condensation try placing the jar on a cool surface so that the liquid tends to be cooler that the parts. I use the lid of my old freezer as it is poorly insulated. Don't get any liquid on the parts as this removes the blue. Make sure everything is degreased of course and boil and card between cycles as usual.
Pete
 
JasonS said:
Try Youtube and search "nitric acid" tons of demos.
Click to expand...

I had considered making nitric acid, but would prefer to mess around with the chemicals as little as possible. The demos are pretty neat though!

pjs said:
Try 2 parts water to 1 part muriatic in a jar (don't need much) and suspend the parts from the lid. I've had good results and have found that I can rust twice per day. Usually takes 5 or 6 cycles. A plastic peanut butter jar works well. Heat up mechanics wire to melt holes in the lid and use the wire for hanging. If you have a problem with condensation try placing the jar on a cool surface so that the liquid tends to be cooler that the parts. I use the lid of my old freezer as it is poorly insulated. Don't get any liquid on the parts as this removes the blue. Make sure everything is degreased of course and boil and card between cycles as usual.
Pete
Click to expand...

Thanks for the tips! PM sent
 
Apart from using nitric rather than HCl, also degrease the metal with lye before you start rusting. For that matter you can probably get a good rust initiated with soldering flux; the stuff that looks like vaseline. I notice any iron that it is left on, seems to rust within a day. Once the rusting is started, wash it off with lye and switch to acid. Finally you will probably need to use boiling water to turn the rust from brown to brownish black. You also want to do your carding with wet steel wool. Dry steel wool is too aggressive.

cheers mooncoon
 
The soldering flux is a good idea. I'd be thinking a thin film wiped on with a clean cloth... sound about right?

I actually suspect I just degreased wrong, as I wiped a piece with a gloved finger this afternoon and it's rusting, unlike the rest of the pieces... I'm going to degrease all the parts again and see if that solves the problem.

Planned process is get rust going, boil pieces in water, card with degreased wet fine steel wool and repeat.

I read somewhere that a little baking soda or hydrated lime was good to add to the final boil to neutralize the acid. That sound about right?
 
This is the first I've heard of this process for bluing, how does it compare with hot or cold bluing? Any pictures you have would be great.
 
Haha - I'll post when I actually get something worth taking a photo of :p

It's slower than cold bluing or chemical bluing, but can be done at home. As I'm learning, it's pretty sensitive to proper cleaning (far far more so than cold bluing) and you have to watch out for condensation forming on the parts and blocking the rust...
 
I've been thinking about this a lot lately. What I intend to try is having seperate containers of Muriatic Acid and water inside a rusting box or container. As long as the humidity in the box is high (and leaving it out in the sun should accomplish that) the metal should start to rust - God knows that if you leave muriatic acid open in your shop it will rust everything in sight! What I've discussed with the Old Man is fabricating a container out of black ABS pipe and setting same in a paint can full of concrete (to avoid tipping). If you make the container out of 6" pipe and set a 2.5" pipe in the center (again, anchored in concrete) you can fill the void of the 6" pipe with water and fill teh 2.5" pipe with Muriatic Acid. Then you can set a top on the piece of varying heights (just use a 6"-6" coupling and tailor the height to the piece you're working on - knife blade or barreled action). Cap the top with a 6" ABS cap (don't glue this on!) and you can insert a hook through the cap to hang your material on. Put the material to be blued on the hook and place same in the tube. Then after you fill the water and acid reservoirs you can set the top tube on the bottom in the coupler. The black ABS should create high humidity and react with the acid to rust the bejeesus out of the metal. In good weather you should be able to get two rusts a day out of such a setup. I'm anxious to try when I get to the farm this summer.

Once you get rust you have to boil the parts in distilled water (apparently there are minerals in regular water that will discolour the bluing) and once the rust turns black you card it off with degreased steel wool , dry and repeat the process.

I've heard, but not experienced, that a mirror polish may be harder to get to take the rust than a slightly "rough" finish (say 600 or 800 grit). You might try that with your process. I'm not sure that there's any benefit to "painting" the parts with acid. That will likely cause runs or drops and lead to an uneven finish. I know they recommend it when using the various rust bluing formulas available on the market, but I think you're better off with clean, dry metal for a acid-vapour bluing like this.
 
Wally,

A couple of years ago, I did some experimenting with rust blueing some small parts and a barrel. I read about the various nitric-acid/iron filing based rusting solutions, but had no luck finding a local pharmacy that would sell me the chemicals, so I decided to experiment a bit with various ratios of diluted muriatic acid and hyrdrogen peroxide. I consulted with a coworker with an MSc in chemistry before doing any mixing, so please be careful and make sure you know the proper way to mix water and acid.

I polished the metal with wet/dry sandpaper up to 400 grit and then put a final even satin finish using a grey 3M sanding sponge that I bought from an autobody shop. As a previous poster mentioned, you don't want to go much finer than 400 grit or the solution will bead as soon as it hits the metal. Even for vapour rusting there's probably not much point to go finer than 400 grit since the rust itself is grainy/powdery.

After polishing, I wiped the metal with Simple Green and then boiled it in water with a few drops of Dawn. From this point on, I was very careful to only handle the metal with clean nitrile gloves and carrying wires.

For small parts, I daubed the solution using a dampened 100% cotton ball and then transfered the parts to hangers in my bathroom. I then took a shower and that was enough to get the rusting started. I let each cycle go 18-24hrs before boiling in reverse osmosis purified water (the bulk stuff from Thrifty's grocery) and then carding with degreased 0000 steel wool.

A couple of hints about the boiling:
1) use clean water for each boiling cycle and clean your pot well before boiling --- you want to avoid any and all oil contamination on the metal
2) make sure that the metal is suspended off the bottom of the pot and completely covered with water; otherwise, you will get a visible line on the metal where it exits the water or heats unevenly
3) boil just long enough to convert the red/brown rust to black, overboiling will cause mineral stains or secondary rusting which will *not* turn to black

For subsequent cycles, apply the solution very lightly; using too much pressure or solution will cause the previous rust layer to be rubbed away.

For large parts like the barrel, I used a Coleman cooler to contain the metal. I placed a dish of my solution and a dish of warm water and closed the lid. For the first couple of hours, I changed the dish of warm water as it cooled down.

=====

My results where so-so. The small parts came out great with a deep black colour and satin sheen. The barrel ended up not so nice and looked similar to the rough finish that Remington puts on their 700 SPS barrels. I blame the rough finish on the barrel to condensation that caused an increased concentration of acid to create micro-pits. I like a previous posters recommendation to keep the solution/vapour cooler than the metal to prevent this occurrence.

I'm also suspicious about impurities in the muriatic acid causing the finish to be rougher and uneven. I used "industrial" acid from Canadian Tire, but in the future I'd try to find some pharmaceutical grade HCl.

One thing that I'm still curious about is the role that the additional ingredients play in the well-known rust blueing formulae (e.g., the iron filings). My results were black and had no other hues, which might be a result of using straight acid.

Since then, I've started using Radocy's express rust blue and have had excellent results. It's a much faster process and the result seems to be a finer finish to the metal. I have a big bottle of it (more than I'll ever need), so you can have some if you want to give it a try. I also have a bottle of Laurel Mountain's rust brown/blue, but haven't had the opportunity to use it.

I enjoyed the rust blueing and think it's the perfect finish for the home hobbyist. The next project I work on, I plan to make a proper humidity cabinet. I think the key to a good rust job is cleanliness, consistency, and short rust cycles to keep the rust as fine as possible.
 
I've never tried the 'fume method of rust bluing. I fact I hadn't even heard of it until this thread. Interesting concept.

All of my slow rust bluing has been done using a version of the "Browne of Swiss Federal Armoury" or Barrel Brown and Degreaser from Laurel Mountain Forge which apparently is a version of the Swiss Brown but with a strong detergent added.

Both of these solutions provide a very nice black with as few as three applications. In fact, on a pre-64 M70 I just completed, I had complete coverage on the barrel with only one application of Laurel Mtn. After four applications, the rifle was done.
 
If your looking for Nitric Acid or any other chemicals I would try Sigma Aldrich, one of the worlds largest chemical distributors. We order from them in the lab where I work and most things arrive by courier within 1 to 2 days. I would be careful as to how strong of a Nitric acid solution you get though as these are lab grade chemicals so some are quite strong. 1N Nitric Acid is about $20 for 450mL, or $40 for 2L.
 
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