Propane heat from a torch (Working One) can reach 900 to 1000 deg C and with copper and bronze and maybe some thin steels produce different effects Rainbow patterns. The neat Red-orange-yellow-pink color on the copper after it been electroplated in acid and added to a 1 L beaker with HCl 31.45 percent with oxygen pumps to create small amounts of chlorine gas that partly dissolve in the HCl.
This turns the layer orange-pink making it prone to heat ionization method.
Citric acid and Potassium monobisulfate are corrosive salts/acids
Hydrochloric acid is a voltile-corrosive acid.
Chlorine is a highly toxic gas work in a well-ventilated area.
Propane can cause fires, explosions, or death is misused.
Phosgene produced sometimes with Propane and chlorine side-products is Highly toxic See warning in future steps. The final step that is.
Fire Protocols must be fully in place while working with Propane.
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Step 1: Different Effects With Copper and High Heat.
To make Brass Heat up 3 g of Zinc Powder in 5 g Lye (KOH or NaOH) with boiling and keep an eye out for zinc power clumping onto the copper. Wait 40 minutes then to a clean pan (Steel) apply the zinc coated pipes to high heat with Propane.
You should get golden brown colored pipes (Brass). If you want Red-Orange-yellow Pipes you need to add carefully 0.1 moles Sodium bisulfate for 1 hour clean off and heat up again and repeat until you get corrosion type colors.
Here what it should look like Golden color. The better the color the more impressive the results.
Videos on How to use regular Propane 1000 deg C on copper.
Last Pic Butane at 1000 deg C so Propane at high heat can be used if the heat is "Controlled". Controlled heat seems to be the KEY.
A thin copper pipe is cleaned with acid and chlorine and washed with tap water and exposed with a clamp to high heat (moving it around a bit) for 30 minutes. If done again better results could occur!!
Step 2: Making Steel Bolts Mildy Rainbow. Acid (Chlorine-HCl) Prep AND Propane.
It makes more sense to convert the steel with 25 percent HCl and the rest dissolved Chlorine and Oxygen (Pump In the water). Done for 20 minutes the steel immediately fizzes and in 20 minutes it is black in color.
Open up the fume device (Important turn off the pump) and carefully without breathing in Hydrochloric acid fumes and Chlorine use a steel rod or glass to remove the bolts from the solution. Must be done in a well-ventilated area due to toxic fumes!!
Get the Propane stove on to max for 20 minutes and to lighten the color (acid-chlorine dose dependant) carefully add 1 ml of Chlorine water: HCl to the hot surface. Be very careful since acid will spray wear Preferably a face shield due to the hot acid spraying around! If too much is added it may be TOO light in color. Don't inhale any fumes either from this protocol.
Thinner pieces of stainless steel that been corroded can be soaked for an Hr in HCl:Chlorine: Oxygen water mix as before and dried off then heated directly with the flame and the metal will turn Red Hot color and thus turn different colors!!
An attempt to make a dog chain Rainbow it failed! Too thick steel and not high enough heat. The color was temp only lasting an hour or so. After that, it was barely noticeable under bright light.
Step 3: Final Word to Get Better Results.
I think my Propane torch and stove were NOT high enough to give Rainbow colors. I could with multiple uses get Blue-Purple and Red-pink-orange, etc on copper and rainbow effect on steel. If you repeat and your getting in trouble or cannot get pretty colors. Here is a recommendation.
Use a MAPP Propane gas with Oxygen tank to reach 1800 deg C thus you can heat up and get BETTER results than I did. I am showing that Potentially low heat propane with other tools can give pretty results too. Even if the MAPP gas and Oxygen cost 100 dollars that may be worth it to get pretty results.
Bonus if you have a furnace!
Some warnings about MAPP gas, Propane, and soluble chlorine. As a safety note chlorine as a liquid should never touch the flame of your Propane it will form chloro-hydrocarbons and at that heat will decompose to deadly Phosgene gas (COCl2) yes, the same gas that killed 85 percent of people in WW1 as a deadly gas.
Always afterward wash the steel or copper with cold water and dry so that only trace amounts of chlorine is present (trapped into the metal). Phosgene has a lethal dose of 40 mg per L -and Immediately Dangerous to Human life is near 2 mg an L and above. Compared to the lethal dose of chlorine 1 g per L and the fact that Phosgene numbs the olfactory sites you eventually will not be able to smell it until it reaches Potentially lethal concentrations.
Please TAKE my word never allow chlorine that forms HOCl with Propane. Phosgene can have a delayed and chronic - potentially fatal effect from 1 hr to 10 days or more!!
As I stated color annealing steel, copper and brass and bronze can work. It takes Practice and for thin plates regular propane may be used but if it is big MAPP and oxygen or Acetylene and Oxygen may be needed. Also, the metal should be as shiny as POSSIBLE!
Thin metal (Prefer new steel- 0.03 inches to 0.05 inches) and flat can be changed into multiple colors with Propane alone. Anything thicker may require MAPP gas and Oxygen or more.
Also very clean Metals like copper or brass or steel is essential.
Good luck with your color annealing! :)