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hot salt vs rust vs charcoal bluing

Discussion in 'Gunsmithing and Repairs' started by grafsk8er, Feb 22, 2010.

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  1. grafsk8er

    grafsk8er Member

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    what exactly are the differences? and is any more preferable, longer lasting, more aesthetic etc? thanks
     
  2. HisDivineShadow

    HisDivineShadow Member

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    Hot salt = nitre bluing? If so that is sinking your piece into 600 degree molten potassium nitrate, sometimes it's also mixed 50/50 with sodium nitrate to lower the melting point. Depending on the temperature you will get anything from a straw yellow to a peacock blue finish. It is very pretty but not very durable. The very high temperatures also makes it unsuitable for parts that will contain pressure. Using it on parts is the most common.

    Charcoal bluing I have no real info on but I know it produces a similar peacock blue as nitre bluing and that it is not as durable as caustic bluing.

    Slow rust bluing is a very labor intensive method where you repeatedly rust the rifle in a special way, it produces a finish similar to factory caustic bluing, depending on how well you have done this process it could look far nicer too. It is also far more durable than any of the above mentioned processes, it is also more durable than regular hot caustic bluing.
     
  3. dfariswheel

    dfariswheel Member

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    Modern hot salts bluing is actually boiling the metal in a tank full of commercial caustic hot salts and distilled water bluing compound.
    This is different then nitre bluing.
    In this process, the metal is first boiled in a tank full of a cleaner to clean and pre-heat the parts, then they're immersed in the tank full of bluing chemicals for a specific time.
    After they come out they're then boiled in a tank to stop the chemical process.
    This is the modern bluing process and is used by all the gun companies and refinishing services.
    The level of shine is determined by the level of polishing done BEFORE the metal is blued.
    The big difference between a satin black Ruger and the brilliant deep mirror-like blue of a Colt Python was primarily the polishing done before bluing.
    The commercial caustic salts process is the most durable of the blues, and the cheapest to apply.
    Done right and properly polished before bluing and the appearance is outstanding.

    Rust bluing is done by boiling the parts in pure water, removing them and swabbing them with a chemical that causes the parts to rust.
    The rust is "carded" off with degreased steel wool, then put back in the water.
    Each time the rust formed by the chemical is carded off, the blue color gets deeper.
    Rust bluing is a durable blue but has a more satin blue finish instead of the shinier finish you can get with modern caustic chemical bluing.

    Charcoal bluing is any one of a number of similar heat bluing processes in which the parts are usually placed in a steel drum with a mixture of bone meal, charred leather, and other often "secret" ingredients and heated in a temperature controlled furnace.
    When the parts come out they have a deep blue finish that's attractive, but not as durable as the caustic process.
    Colt notably used this type of process in the pre-war days, which was called "Carbona" bluing.
    This process is very similar to the way in which steel is given a color case hardened coating.

    Heat bluing is simply heating the parts until they change color.
    When steel is heated it starts changing to a light yellow color called "straw" then through darker yellow, brown, purple, then to a brilliant blue.
    The blue is a lighter, more delicate color than other heat processes, and is not very durable at all.

    There are any number processes by which steel can be given a blue color, with many of the heat-type processes being very similar.
    Due to the expense and time needed for most of these processes, most guns are blued with the commercial caustic salts process, with the others being reserved for high-dollar custom work or for restoration of valuable antique guns.
     
    Last edited: Feb 23, 2010
  4. Customstox

    Customstox Member

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    There are a few errors in the rust bluing description.

    "Rust bluing is done by boiling the parts in pure water, removing them and swabbing them with a chemical that causes the parts to rust.
    The rust is "carded" off with degreased steel wool, then put back in the water.
    Each time the rust formed by the chemical is carded off, the blue color gets deeper.
    Rust bluing is a durable blue but has a more satin blue finish instead of the shinier finish you can get with modern caustic chemical bluing."

    You start by having your metal prepared and degreased. You then put on a chemical, mainly and acid with cloth swabs. The gun is then left to rust and usually in a humidity controlled cabinet. The metal is then taken out and boiled in distilled water which turns the red rust to a stable ferric oxide that is black. It is then carded off using thin stainless steel wire wheels turing at about 1300 rpms. Then the process is repeated, swab on the chemical, let it rust and boil and card. Often 6 to even 12 coats will be applied.

    It can be a matte finish but that depends on how you prep the metal and how long you let the rust go before boiling. You can get a nice bright shine with a different approach. It is probably the most durable finish and the most expensive.
     
  5. Oyeboten

    Oyeboten Member

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    Good mentions Comstox


    I intend to try the Rust Blue method on an older Model 10 S&W.

    Had not considered using very fine Wire Wheels...


    I have some old Brass Wire ( not Brass plated Steel ), very very fine 6 inch Wire Wheels, which are very kind to extant Blueing, while, yes indeed, removing 'Rust', and I had not even thought of them for use in this Blueing process.


    Thanks!

    That will make things a LOT easier on me
     
  6. Alpacca 45

    Alpacca 45 Member

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  7. 44-henry

    44-henry Member

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    I've played around with charcoal blueing in the past, a lot depends on the temperature, but you can get blues that are exceptionally deep and dark with it, not necessarily the lighter peacock blue that some places tout as "true charcoal blueing". Everytime I've tried it I've always used an electric heat treat furnace and wood charcoal from Brownells, it isn't too hard to accomplish good results, but it does take some experimentation.
     
  8. navyretired 1

    navyretired 1 Member

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    Bronze or brass wire wheels don't work. You need steel or stainless of very fine wire for carding or degreased 4 0000 steel wool. Carding is what you do after boiling the rusted piece it will have a very fine black velvet finish over the whole surface, That is what you are carding off. you have to be gentle and not too agressive with the carding. Don't get discouraged if the first 2-3 sessons don't produce any more that a graying of the metal. The secret is to keep going. It only takes about 1 hour a day, but for 12-15 day's and you can't skip a day when rusting or you can get pitted metal. When they say it's the most expensive, it's because of all time invested not cost of materials.
    I've got a S&W model 27 That has the most beautiful blue job done slow rust style. When knowledgable gun guy's look they say " wow that S&W prewar finish is beautiful isn't it. Real surprises them to find out it's only 8 years old.
    You have to prep the metal right, glass bead for matt and brite polish just like factory. And touch up is done with rust blue too blends perfect. (SLOW)
     
  9. HisDivineShadow

    HisDivineShadow Member

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    I would say the rust bluing process is more durable than hot caustic bluing.
     
  10. Tn Tom

    Tn Tom Member

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    Slow Rust Bluing
    it is a very labor intensive. I use a mixture of muratic, hydrochloric, and water with an oz of iron wire disolved. Usually about 3 hrs in a sweat box (85% humidity and 90F) for 3 hours. Requires 3 - 5 acid wipes. card with stainless wire brush (very soft) I'll try to post some pics of the guns I have done. Its a very very moody process but if something g[​IMG][/IMG]oes wrong just start over. The hardest part is preparing the metal. must be absolutely clean and preped in a cautic bath .
    It takes a very full day once you begin. Begin early in morning and finish in the evening.
    Beautiful when its done. Soft satin like. Color depends on the metal compositions and can look yellowish if the material isnt compatible which does happen. Usually a plum tone. I have some pieces, a barrel or two that hang unoiled in the shop which I dont climate control that much and they have showed no signs of rusting and they were treated 5-6 years ago. Never tried to scratch one. Cant bring myself to do it.
     
    Last edited: Mar 2, 2010
  11. jimmyraythomason

    jimmyraythomason Member

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    While I can't disagree with this because I have never done rust bluing. I have done a LOT of hot salts bluing and know it to be VERY durable.
     
  12. Alpacca 45

    Alpacca 45 Member

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    Muriatic and hydrochloric are the same thing.

    It is the cheapest of the strong acids, but it's hideous stuff to have around, the vapour leaking out of the bottle or spray from it sets everything to rusting and corroding.
     
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