doublegunshop.com - home Forums General Discussion DIY Gunsmithing @ doublegunshop.com Hot plate for nitre blueing ?

I've got more money in my digital controller than I do in my kiln. My small Duncan kiln was only $30 at auction, but I had to spend around $100 on the controller. Wiring it was fairly easy.

Hot plate will work. New ones are junk and kick in and out and don't hold temp. The old ones with the exposed wire coil work good but I like the controllability of gas.

El Garro using sand to level out the rise and fall of the applied heat is not a new idea though I do wish I could say I thought of it, but I would be a couple of hundred years too late. It works so well because sand is a poor conductor of heat so fluctuations are rendered much slower because of the sands poor heat conductivity.
I would like to pass on the origins of using this method of bluing steel only using heat and no other chemicals.
If you look at a very high quality time piece one of the things you will notice is that the screw heads the clock hands are a striking colour of blue, all produced by using heat alone. Now I am sure that at some time or other you have heated a Steel screw in a flame to turn it blue and that colour is fine, now the clockmakers of times past realised that if you polish the screw heads and clock hands to a high polish finish. Then by heating them up very slowly the oxide layer on the metal thickens and the finer the blue colour becomes, so to keep things stable they used sand as a heat buffer. And that is how the screws and hands on old quality time pieces have that wonderful deep translucent blue colour.
Of interest to some folks and may be not others.

Here's a question. If going up to 830 degrees, as Brian pointed out, (which is easily done with a kiln) which is the better medium?

Salts, or Saltpeter, such as stump killer, or is it better to use lead?

Regards
Ken

Thanks again for the input Gents, I've been able to get the salts up to a high enough temp to black a few pins but not managed to get any larger parts past the 'iridium' looking stage, I'd assume that's down to the small heat source , hopefully I can improve things there.
A small kiln or melting pot is starting to sound more appealing, cost may be prohibitive for one large enough to do a long trigger guard though.
That's something I need to look into.
Having ordered the hot plate in a moment of madness (�10-last couple in stock) I will have a crack at fitting an improved thermostatic switch , I believe the temp sensor is fixed to the plate so should be an improvement from the start. I can get thermocouples and all kinds of temp control gear from a guy I know who's an instrument man in the chemical industry (he's helped me out with my caustic tanks already) so should be able to cobble something together and do some trials. If it's fails miserably , a kiln or similar is the next step.
Thank you for all your ideas and suggestions, it's extremely helpful and much appreciated. I will get busy when it all arrives write up the results.

Hi ken, interesting thought about lead vs salts.
Although there may be some nasty fumes from the lead (easily solved with ventilation) could there be a benefit with it in the case of an accidental spill or splash. I believe that salts at that temp can make most organic matter, i.e. wood, paper, cloth burn at an alarming rate.
I know we can avoid this happening by taking care while working but it may add a point in favour of lead.

http://www.sciencemadness.org/talk/viewthread.php?tid=16706

Here's the thread about improving heat control.

I tried the "commercial grade
...ie..expensive type for nitre bluing..wont get hot enough. But it's only 110v, next will be a 220v set up.

Right now I'm using a led melting pot with a pid temp controller

Hi Mike, I read an article about a lyman pot with a pid controller. What a clever bit of kit they are. Did it take many cooling/heating cycles to adjust itself ?
My hot plate hasn't arrived yet but I'm tempted to look for a lead melting pot as I was surprised by the reasonable prices of some models.

If you are doing larger parts, a propane burner and a metal box about the size of a .50 BMG ammo can, and thermometer works well.