metal color change

I need some advice.
I am taking stamped metal parts (nickel silver) and heating them up to about 450 - 500 degrees. Many of them change color from a shiney
silver to a bluish color. This is the effect I want.
Lately, many of the parts are not changing color. When stamped, we use a light coating of kerosene for die lube. Sometimes we run fairly dry.
IS the color change a result of the light kerosene? Is it a function of temperature? What can I do to ensure that all the parts turn bluish?
Thank You,
Wayne
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snipped-for-privacy@yahoo.com wrote:

Clean them. Maybe the oil is keeping the metal from oxidizing? Randy
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On Aug 8, 9:21 am, snipped-for-privacy@yahoo.com wrote:

Generally, patina of metals is controllable. Find your way to a good library and look for Metal Finishing Handbook, there are recipes for these situations. If your alloy doesn't change, minor cleaning/preparation of the surface is all it takes to get a uniform result.
Look up shakudo when you have a few spare moments.
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The color change is a function of temperature, in an air atmosphere. Each oxide (there are several) forms at a different temperature. Some steel alloys don't produce all oxides so they don't show all colors.
Clean surfaces are important for getting consistent colors. The oil could be preventing the oxidation.
-- Ed Huntress
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I assume you are talking celcius, since Fahrenheit temps in that range would yield dark straw to red. At, let's say, 475 C (887 F), you have just about run out of temper colors. So, if you are only approximating this temp range(450 to 500), you may be getting things a little hotter than you used to be doing. You need to be down at about 350 C to get blue, I think. I also agree that the lubricant may be protecting the metal from oxidizing. Lastly, I forget what "nickel silver" is, but I don't think it contains any silver anyway. If it did contain silver, then all bets are off. Isn't it British slang for something like O1 tool steel?
Pete Stanaitis ------------------------------------
snipped-for-privacy@yahoo.com wrote:

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spaco wrote:

I can help on this one. Nickel silver is a trade name for nickel brass. with anything from 5 to 10% nickel. the rest is zinc average 25% the rest is copper. Its used or was for lots of decorative fancy ware and cutlery. as stamped it becomes surprisingly springy. Now as to colouring it. 1. you need to have it clean, have you got any 3M compressed scotchbrite wheels? fine grade. I use them exclusively for metal cleaning.Run Dry of course with proper dust extraction. The you need a soft ie fully oxidised propane flame with your item sitting on a grid of some sort , the flame is applied from undernreath and the burner ,I use a 2in dia slow running clamped onto the stand then as the flame licks over onto the top of your metal youll find it will oxidise to what ever colour yoiu want as the temperature rises. you can do this by eye.. Remove from the grid with a spatula or tongs and place onto say a sheet of ali to cool. repeat. Ive done hundreds this way on copper brass, nickel silver, bronze etc.. Ted Frater Dorset UK.
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You're thinking of "silver steel." Someone posted the makeup of nickel silver (it used to be known as "German silver" in the US). It's copper and nickel, and, in most formulations, zinc.
I posted something dumb in this thread earlier because I didn't notice that nickel silver was the subject. I was thinking steel. However, nickel and copper also form oxide colors from heating. I just don't know how the colors relate specifically to temperature.
-- Ed Huntress
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