- Metal hardness matters: I am assuming metal hardness matters when it comes to cleaning soldering tips with metal wool.
- Chrome tip quality and material: I am assuming (good quality) soldering tips are chrome plated/electroplated.
So, for cleaning soldering tips:
[metal hardness(soldering tip)] > [metal hardness[metal wool)];
I.e., the hardness of the soldering tip must be greater than the hardness of the metal wool.
Now, for metal wool, traditionally, brass wool is used. However, copper wool does exist.
For [metal wool(x)], x = brass, copper, etc.
My particular case and example:
On sponge wool available: I am using copper wool. In this example, I'd like to consider copper hardness. (This copper wool might be copper-coated steel-strand-cored wool). Does copper wool work effectively to remove oxidation from a soldering tip.
On the black oxidation: Being more a technical hobbyist than an experience technician, I've used and abused my soldering iron tip in that I've used it for other projects, like makeshift plastic welding. This did not come without consequence. That consequence was the heavy, burnt, carbon-containing material and debris collected on the surface of the shaft and tip of the soldering iron, with black oxidation on the tip. However, other than that, I've had very little use with the soldering iron and have treated it pretty well--no plating has eroded so the areas that have been cleaned are wettable with solder.
One more detail: clarification on intent of question: This is not a question of a non-traditional sponge is better; rather, if a brass sponge is safely interchangable/fungible with another type of sponge. Hence the angle of my answer below.