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Thread: Hot Bluing
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10th Apr 2017, 01:19 PM #1Golden Member
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Hot Bluing
A friend of mine has a number of old firearms and asked if I would have a go at the hot bluing process for him, so yesterday I mixed up a small scale amount of salts from the simplest formula I found online (5lb sodium hydroxide, 2.5lb potassium nitrate, 1gal water, I actually used potassium hydroxide because I have it on hand) and ran a couple of test pieces.
The first was a newer looking P&N HHS drill bit that took the blue quiet well considering the only prep work I did was wipe it down with some metho.
DSC_3307.jpg
The second test was a piece of hot rolled mild steel I turned and polished up, it came out a little bit blotchy at one end, I suspect the cause was while I was bluing some water evaporated from the salt mix exposing areas of the part to air, I also noticed the galvanised tie wire I used to hang the part left a mark so I'll have to use something else from now on.
The area where the blue took is perfect, I couldn't ask for better, I just need to get it even over the whole part.
DSC_3315.jpgDSC_3314.jpg
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10th Apr 2017, 01:49 PM #2
I've always wanted to try hot bluing, but can't get hold of potassium nitrate ... where did you get it?
Cheers.
Vernon.
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10th Apr 2017, 02:05 PM #3Golden Member
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Hi Vernon, I got a 25kg bag of potassium nitrate fertilizer a few years ago from the nearest rural supplies store, cost me about $40
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10th Apr 2017, 02:07 PM #4
Its very difficult to get potassium nitrate now - if at all. It used to be a common fertiliser. Farmers also used it mixed with diesel to surgically remove tree stumps from the ground. It cn also be used as a rocket propellant and for fireworks..... So now you need a license to buy it and farmers went on to alternative fertilisers instead.....
Cheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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10th Apr 2017, 03:09 PM #5
Hence why I was asking ... I thought there may be an alternate supply small quantities.
I have been using parkerizing instead.Cheers.
Vernon.
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10th Apr 2017, 06:34 PM #6Golden Member
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To be honest I was very surprised they sold it to me, I think the only reason I was able to purchase it at the time was because I chanced upon a staff member who didn't know any better
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10th Apr 2017, 07:58 PM #7Golden Member
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Umm, I think you blokes might be thinking of ammonium nitrate, potassium nitrate is pretty harmless on the scale of things and as far as I'm aware freely available.
Quick google found this:
Potassium Nitrates
I would have thought the green place would have it in smaller quantities, try looking for saltpetre or perhaps potash, I can't remember but potash might be a different potassium salt.
Cheers,
Greg.
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10th Apr 2017, 08:44 PM #8Golden Member
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Yeah, you'll never get your hands on ammonium nitrate and I'm sure it won't be long before potassium nitrate suffers the same fate, better go buy another 25kg bag
Potash is potassium sulphate
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10th Apr 2017, 09:03 PM #9Member: Blue and white apron brigade
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With a little time and patience it can be extracted from urine.
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11th Apr 2017, 09:42 AM #10
Stop taking the Bob.
Cheers.
Vernon.
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15th Apr 2017, 07:04 PM #11Golden Member
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Had another go at bluing today, this time I degreased with acetone before submerging in the bluing salts, I think the results speak for themselves
DSC_3330.jpgDSC_3337.jpg
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16th Apr 2017, 03:15 AM #12(5lb sodium hydroxide, 2.5lb potassium nitrate, 1gal water, I actually used potassium hydroxide because I have it on hand)I got a 25kg bag of potassium nitrate fertilizer a few years ago
What temperature and what length of time?
I'd like to have a go at it. Looks really nice.Cheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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16th Apr 2017, 03:42 AM #13Golden Member
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Hi Joe
I used 5lb potassium hydroxide, 2.5lb potassium nitrate, 1gal distiller water (although some water did evaporate while bluing), the time was approximately 25 minutes and the temp hovered around 140 °C, it climbed a little as the water evaporated.
I switched out the sodium hydroxide in the formula for potassium hydroxide because I have some on hand and I doubt it makes any difference, if I were to scale up the process I would use sodium hydroxide because it's considerably cheaper than potassium hydroxide
Cheers
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16th Apr 2017, 03:56 PM #14I break stuff...
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Results look fantastic! What are you actually heating the solution in?
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16th Apr 2017, 05:56 PM #15Golden Member
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it should be done in a black steel/iron vessel and alloys should be avoided due to the risk of leaching that could contaminate the salts, but for testing I've just been using a stainless steel pot on the stove
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