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  1. #16
    BobL is offline Member: Blue and white apron brigade
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    As proposed a few pics of the fume bluing setup.

    The tank/chamber is a 50L plastic drum with a rubber gasket and clamp seal.


    Inside the tank are 3 plastic containers.

    one is about half full of water, other two are about 1/5th full of acid. One is concentrated HCl and the other is concentrated nitric acid. In this photo the lids of the acid containers are screwed back on to save the fumes.

    The white PVC pipe rungs are what the objects being blued are hung from using wire hooks.

    The recipe I used was as follows.

    1) Polish the metal to as high a shine as you desire for the final finish. The smoother the finish the more protective the coating will be. Mine have only been polished using a scotchbrite wheel so it was more of a matt polish.

    2) Wash the oil and first from the metal parts by boiling is a weak (5%) solution of sodium carbonate [(Foot spa salts) a 500g bag costs about $5 a bag at coles] for an hour

    3) From this point onwards handle the parts with rubber gloves. I use those disposable latex type. Rinse the parts with distilled water and transfer to bluing chamber. make sure the chamber is sealed to keep in the fumes or they will corrode all ferrous stuff they come into contact with.

    4) After the parts have formed a coating of rust [this can take anywhere from a couple to 12 hours] remove from chamber and place into a container of boiling distilled water. I use a large stainless steel saucepan on an old electric frying pan. Boil for one hour, rust colour should go black.

    5) Remove and allow parts to dry. Then remove the loose "soot", which is black iron oxide,from all surfaces using a fine stainless wire brush and/or fine steel wool. Fine steel wool works well on flat surfaces but brushes will work better on threads and into nooks and crannies. Don't be worried about using the wire brush to get the soot off. At this point the steel might only have changed to a medium grey.

    6) Repeat steps 4 and 5 until the desired depth of colour is obtained. This means somewhere between 10 and 15 cycles.

    7) finally Heat the parts in hot oil (I use new engine oil in another stainless steel saucepan on the electric frypan) for a couple for hours. Remove parts from oil, let cool and wipe off excess oil. For maximum protection the parts should be kept lightly oiled. If the develop surface rust they can be re-blued as per new pieces.

    Thats it. It's a very slow process but the finish is supposed to be one of the more robust of the bluing methods. It's not used much because it is so slow.

    The one snag for the average joe is getting nitric acid is not that easy.






    the protective cos

  2. #17
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    Hello Bob,

    Would it be feasible to scale things down? The reason I ask is that the bits I would make that would benefit from the fuming would tend to be small, bolts, screws etc. and not a large quantity. The cast iron fittings that I've made, whilst not large, have a rough, off the cutter finish. Not the finish suitable for fuming.

    How small a volume of nitric acid could be used?

    BT

  3. #18
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Anorak Bob View Post
    Hello Bob,

    Would it be feasible to scale things down? The reason I ask is that the bits I would make that would benefit from the fuming would tend to be small, bolts, screws etc. and not a large quantity. The cast iron fittings that I've made, whilst not large, have a rough, off the cutter finish. Not the finish suitable for fuming.

    How small a volume of nitric acid could be used?

    BT
    Absolutely it can be scaled down - the reason I went for a 50 L tank is because I have a couple of long things I want to have a go at (no they are not gun barrels!). My first setup was a 10 L plastic bucket, but it could be scaled down even further. In terms of amounts of acid required, Guy Lautard talks about using a few ml on a glass plate or in a glass jar as being all that is required. Be careful not to directly mix the liquid HCl with the Liquid HNO3 or Cl2 gas may be generated and that is not nice.

    Just to show the extent to which I am prepared to go to get this right I installed an improved water purification system - mainly for my coffee machine, but a side benefit will hopefully be to really nail this bluing business. A pic and some details here. If this all really necessary - probably not but I want to make sure I have no excuses.

  4. #19
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    Quote Originally Posted by BobL View Post
    Absolutely it can be scaled down - the reason I went for a 50 L tank is because I have a couple of long things I want to have a go at (no they are not gun barrels!). My first setup was a 10 L plastic bucket, but it could be scaled down even further. In terms of amounts of acid required, Guy Lautard talks about using a few ml on a glass plate or in a glass jar as being all that is required. Be careful not to directly mix the liquid HCl with the Liquid HNO3 or Cl2 gas may be generated and that is not nice.

    Just to show the extent to which I am prepared to go to get this right I installed an improved water purification system - mainly for my coffee machine, but a side benefit will hopefully be to really nail this bluing business. A pic and some details here. If this all really necessary - probably not but I want to make sure I have no excuses.
    I just had a read of the coffee thread. Serious stuff Bob.

    Where could I purchase a small amount of nitric acid and does it and the hydrochloric acid need to be of a particular quality? It has been more than 40 years since those chemistry lessons at Hollywood High and even then little sunk in.

    BT

  5. #20
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Anorak Bob View Post
    I just had a read of the coffee thread. Serious stuff Bob.

    Where could I purchase a small amount of nitric acid and does it and the hydrochloric acid need to be of a particular quality? It has been more than 40 years since those chemistry lessons at Hollywood High and even then little sunk in.

    BT
    Ah, getting conc nitric is not so easy these days, perhaps we should discuss this by PM?

  6. #21
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    Hi, I've just read the bluing thread and since starting bluing small arms in the late '60s I have had a lot of experience with hot blue "blacking" cold blue "Neidner process" and browning which is "Neidner" without boiling between rusting cycles.
    The attached photos show "Neidner" bluing and browning results before and after plus the stainless tanks and hot blue mixture.
    I was a chemist, now retired so have a good understanding of the process without using "... ear of bat or dragons blood...". So if anyone has any questions I'd be glad to help from experience untainted by myth and .
    Rob
    Stainless Tanks.jpg B Sidelock After.jpgA Sidelock Before.jpgPerc Before.JPGPerc. After.jpgx Hot Blue.jpg

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