Blueing

Years ago, when i spent most of my school days in the enginnering workshop we used to blue a lot of the work we made. If i remember we heated the part up and dropped it in an oil solution, loved the smell

So whats the modern equivant as i fancy blueing some of my work now?

Clockmakers still blue their screws the same way as always by heating the screws whilst laying in a bed of brass swarf ( heated underneath) until they turn blue then quench in oil. Alternatively you can black your parts chemically, just google blackit solution.

Any thin clean oil will do. The colours develop just by heating to tempering heat and stopping at blue. The oil prevents the process from continuing by cooling the part and providing an oil film to protect the surface. The colour comes from the thin oxide layer developed on the surface when heated and is an optical phenomenon caused by interference which is why the colours change according to the thickness of the oxide layer.

Oil does however make the surface look blacker presumably by mopping up the blue photons somewhat.
regards Martin

Edited By Martin Kyte on 28/03/2023 12:33:34

Cheers guys.

Did a bit of Google work and see that gunsmiths blue their barrels using **THIS**

I also found a good video on how to use

This can be a confusing term as petro1heads post above compared to bernard towers post which are both called blueing.

See Clicksprings video.

If you can get hold of low temp heat treating salts then the process is much easier to get repeatable. I had to buy 20kg bag, with a minimum £50 pallet delivery... I haven't used em much but I hoard them.

The thing about bluing is how thick the protective layer needs to be.

An attractive thin layer suitable for decorative purposes is achieved as described above, but it's not hard wearing.

Deep hard-wearing bluing requires heat and repeat treatment with nasty chemicals, such as molten Nitrates. Coild be done, but not really a home workshop process.

'Cold Blue' is a safer alternative, often based on Selenium. Much used to touch up worn firearms. The resulting layer isn't particularly tough, but it's easily redone.

A thicker protective layer can be achieved by plunging red-hot metal into dirty engine oil. Results vary, black rather than blue, and unlikely to be pretty.

Dave

I have used a cold bluing paste which seems to be quite resistant to abrasion and that is Birchwood Casey Perma Blue which can readily obtained from the this site. The depth of colour can be controlled by the length of time that the paste is left on the metal, this can be a bit variable so requires a bit of experimentation to get a even depth of colour

Martin

So its a toss up between these three

Edited By petro1head on 28/03/2023 15:44:35

Gun barrels aren't cold blued they are hot blued/blacked, if a gunsmith used cold blueing it would just be a minor mark or scratch they were trying to hide. Not used or found a decent hard wearing cold blue and I've tried over the years.

I used the Nickerson Cold Blue on all the toolholders I made. Got pretty good results with it. Parts need to be very very clean. I warmed them up a bit till they were just hot enough to handle then duncked them in the solution till they looked about right. Then oil and wipe over. Look very good.

I got good results on another job after reusing the solution.

regards

I'm really not being facetious but I wish some folks posting queries would first try the site's "Search for" box. There's already a wealth of information and advice on the subject - "Blueing".

Whichever method is adopted, worthwhile protection is possible by the (regular?) application of black shoe polish to the metal surface followed by light buffing.

opps

Edited By petro1head on 28/03/2023 21:19:06

Wheb someone starts a reply to a post "I am really not being facetious" it usually means they are

I did a search and there were only 7 replies.

There are a total of 87 replies according to the search box. Yes, there may be repeat postings included in that total. My point was that there's useful information already on the site.

Well thats very strange as i hva just searched "blueing" again and only get 7 topics

Edited By petro1head on 28/03/2023 21:36:16

So we are both right, 7 topics and x number of posts.

well i think we have covered that

Well, you missed this one,

Rob

Links to https://www.model-engineer.co.uk/forums/postings.asp?th=177264

Cheers, ordered some of the Nickerson from Amazon

Edited By petro1head on 28/03/2023 22:35:54