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NedsHead
10th Apr 2017, 01:19 PM
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.
367419

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.
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Vernonv
10th Apr 2017, 01:49 PM
I've always wanted to try hot bluing, but can't get hold of potassium nitrate ... where did you get it?

NedsHead
10th Apr 2017, 02:05 PM
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

jhovel
10th Apr 2017, 02:07 PM
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.....

Vernonv
10th Apr 2017, 03:09 PM
Hence why I was asking ... I thought there may be an alternate supply small quantities.
I have been using parkerizing instead.

NedsHead
10th Apr 2017, 06:34 PM
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:)

kwijibo99
10th Apr 2017, 07:58 PM
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 (http://www.campbellsfert.com.au/potassium-nitrates.aspx)

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.

NedsHead
10th Apr 2017, 08:44 PM
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:D

Potash is potassium sulphate

BobL
10th Apr 2017, 09:03 PM
With a little time and patience it can be extracted from urine.

Vernonv
11th Apr 2017, 09:42 AM
Stop taking the Bob. :D

NedsHead
15th Apr 2017, 07:04 PM
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
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jhovel
16th Apr 2017, 03:15 AM
(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 did you actually end up using?
What temperature and what length of time?
I'd like to have a go at it. Looks really nice.

NedsHead
16th Apr 2017, 03:42 AM
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

Jekyll and Hyde
16th Apr 2017, 03:56 PM
Results look fantastic! What are you actually heating the solution in?

NedsHead
16th Apr 2017, 05:56 PM
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

steamingbill
17th Apr 2017, 11:58 PM
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


At 140 degrees Celsius is the solution actively boiling ? ie bubbling and spitting and splashing droplets ?

Bill

NedsHead
18th Apr 2017, 01:57 AM
Hi Bill, at that temperature it's simmering, with all the salts dissolved in the solution it doesn't "bump" like boiling water does at 100°C but it does spit small droplets around where it's being heated and release tiny caustic particles into the air that sting when they settle on skin, it's a well ventilated, covered skin and goggles affair

wheelinround
18th Apr 2017, 04:30 PM
:2tsup:

Mike4
24th Apr 2017, 08:12 PM
This would be a good way to make shop made tooling last longer .And look better .

Michael

jhovel
18th May 2017, 07:48 PM
I finally got some Potassium Nitrate yesterday. It was a special order and I had to leave my ful name, address, phone and license number to get it.
Seems nobody bothers to stock it anymore because of these requirements.
I won't have a chance to try and blue anything for a week or so, but will post the results here when I do.

NedsHead
18th May 2017, 08:39 PM
I look forward to seeing your results Joe, it's pretty pathetic what you had to go through just to get it, lets hope counter terrorism don't swoop your house over a bag of potassium nitrate lol

steamingbill
18th May 2017, 10:05 PM
I finally got some Potassium Nitrate yesterday. It was a special order and I had to leave my ful name, address, phone and license number to get it.
Seems nobody bothers to stock it anymore because of these requirements.
I won't have a chance to try and blue anything for a week or so, but will post the results here when I do.


I've tried too and anywhere I go they just say "No cannot get it any more - people were doing scary things with it"

When I was a kid we could get Kwikcure from the local supermarket which was then used to cure meat and was pottassium nitrate

This mob might be worth a try - am off on holidays and will try when I get back.

kno3 potassium nitrate australia (http://auschems.com/index.php/potassium-nitrate-kno3-ar-grade.html)

Bill

NedsHead
18th May 2017, 11:08 PM
15 bucks a kilo, ouch... How much did you end up paying for a bag Joe?

jhovel
19th May 2017, 02:43 AM
I paid $71.40 for 25kg.
Happy to share, if someone else wants a couple of kg ($3 a kg + postage).

Retromilling
22nd May 2017, 12:56 PM
Yes they are talking about ammonium nitrate as a fertilizer however potassium nitrate is even more dangerous .
You want Sodium Nitrate not Ammonium or Potassium nitrate .

NedsHead
22nd May 2017, 01:05 PM
How is a Potassium ion "even more dangerous" than a sodium ion? what is your measure of danger?

Retromilling
22nd May 2017, 02:31 PM
Potassium nitrate is a better oxidiser if it gets heated up by a fire . On it's own it's not so bad . It is used in explosives and some rocket fuels so it is very dangerous if it gets going in a fire .

jhovel
22nd May 2017, 11:03 PM
All three are just fertilisers and meat tenderisers.
Nothing dangerous about them at all - until you deliberately mix them with a fuel which they can oxydise. The mixtures and methods are not trivial and require research or reasonable chemistry knowledge. It is no more complex to make explosives or rocket fuel by many other means without resorting to fertiliser.....
But these were easier to control (than, say, pool chlorine.....)

Anorak Bob
23rd May 2017, 09:25 AM
Hey Joe,

I'll put my hand up for a couple of kilos if it's still available.

Bob.

Retromilling
23rd May 2017, 11:21 AM
Anyway it's not Potassium nitrate you need in a bluing formula it's Sodium nitrate . To get the blotchy affect out you may need to degrease the metal before bluing it.

NedsHead
23rd May 2017, 12:34 PM
I've read up on a few bluing formulas and most called for potassium nitrate, some used ammonium nitrate because of availability but the process had to be done outdoors due to ammonia fumes, any nitrate salt will do the job, and I'm sure sodium nitrate will work but potassium nitrate, being non hygroscopic and non fuming, is more stable in the formula compared to sodium/ammonium nitrate.

Hope this helps

desbromilow
6th Jul 2018, 11:40 PM
so once the hot tank has been made, and the solution used, is there any special storage requirements?
I recall we had a hot bluing tank in SHS, and the teacher just kept a lid on it most of the year, but I never knew if there was fumes causing corrosion, or if the mix had to be dumped each year, etc.
I imagine the salts would need to be renewed/ added to over time, but if the tank was only used once every 3-6 months, is there any storage considerations needed?

FYI - been a while since I bought potassium nitrate - but the hydroponics people seem to have good quality fertilizers at reasonable prices...