I need to anneal some Aluminium Bronze blanks, about 30 mm in diameter and
3-5 mm thick.
1.If I heat them to a cherry red colour, what kind of pickling solution can I use to get them to come out a nice yellow colour.
Is it best to go from cherry red straight to the pickling solution or should I let the pieces cool first then put them into the pickling solution?
What solution should I use for Copper?
I have concentrated Ferric Chloride on hand as well as HCl but I don't want to experiment with them. I use "Tarn-X" for a pickling solution when I anneal sterling silver and 22K gold, but it doesn't seen to do much for the copper, and I know it wouldn't work for the aluminium bronze.
Again, I don't know about Al bronze. With copper, quenching in plain water will knock off most of the black oxide. Then the piece can be placed in the pickle to remove the remaining red oxide. Quenching in the pickle shouldn't hurt the metal, but doing so would likely lead to splattering of the pickle and/or the release noxious fumes/steam, so I wouldn't recommend it.
A traditional pickle for copper is sodium bisulfate (sold under the brand name Sparex for pickling, but also available as pH Minus at pool supply or hardware stores). A warm solution works faster. You can also use dilute (10% or less) sulfuric acid, though it's a bit more hazardous -- don't use it if you're not familiar with the appropriate precautions for handling acids. Be aware that either of these will eat holes in your clothes. They'll also etch the copper if it's left in the solution too long. Don't use steel utensils to retrieve things from the pickle, unless you want them copper plated.
Hum - some odd things - I have Cast Bronze - and will give some for that. Perhaps it will be valid. Only a test by you can tell.
"The colouring, bronzing and patination of metals" by Hughes and Rowe. British printing...
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member
Kyle Mutcher wrote:
Cast bronze. 1.19
One can only guess that once it is cooled - then the following helps. Golden-yellow (grain ehhanced) Satin Note: A reddish ochre color is produced on rough or as-cast surfaces.
The object is immersed in the boling solution. The dark brown layer that forms on the surface should be removed after one or two minutes, by removing the object and bristle-brushing under hot water. It is then re-immersed and the procedure repeated after 2 minutes if necessary. Immersion is then continued to about fifteen minutes, afterwhich the object is removed and washed in hot water, using a bristle-brush if necessary. After thorough washing, it is dried in sawdust, and wax finished when completely dry.
Cool is cool - as it will be boiled for the reaction.
Copper is different from Bronze... There isn't a yellow. The closest color is orange or green. Simple as that.
I suspect the Tin in the Bronze generates the yellow.
With pure copper, if you heat the metal to red, then quench in denatured ethyl alcohol, you will fully anneal while avoiding oxide formation. You will not need to pickle as the metal will appear clean and yellow.
Not sure if this will work for the aluminum bronze alloy but it wouldn't hurt to try. Probably want to use a neutral or slightly carburizing flame to avoid oxide formation.
That's not true of sulfuric acid----it won't dissolve copper, although it does digest copper oxide with vigor. It's the perfect pickle for copper----although somewhat hazardous to use. You can boil copper parts in sulfuric/water and not worry about ruining them.
I'm casting copper and aluminum bronze into a ball moulds then hammering them flat to make a coin blanks. After hammering them I would like to anneal them so that when I strike them with the dies they strike up easier. But after heating the hammered blanks I would like to have as much of the natural untarnished metal colour as possible.