Im a noob with metal working and Id like to know how to get this darken affect like in the following image. The aluminum was punched with metal punchs and the punched numbers are darkened some how. Whats the process for doing that and can that process be applied to other cutting/punching methods? http://imgur.com/6ltw7
Also Im having a hard time understanding the different levels of hardness for aluminum. Im looking to get some pieces to test with from onlinemetals but I dont know whats a good simple one to get that will work for punch sets and other similar marking aspects from a hardness POV.
Lastly (for now) whats the process called when you heat metal up with a torch and discolor the metal? Iv used the process on some zinc covered steel key stocks but can that process also be done on aluminum and stainless steel?
Thanks
On that specific picture of the stamped numbers it appears to me that the numbers were punched then the surfaces sanded on a belt sander afterward, the clean edges of the numbers and just the way the numbers look really make me think that is how that was done. This can be done even by painting then sanding the paint off leaving only the paint in the punched areas, as well as other ways.
Please don’t heat zinc! You can get metal fume poisoning, I have done it and it ain’t nice!
stamp/punch then paint or enamel then sand back surface. looks like 
dont know about hardness of aluminium , i know it comes in different grades like air craft grade that sort of thing.
do you mean hot blueing? doesnt work on aluminium i dont think, defo dont do it to zinc or galvanised that stuff can kill.
hope this helps
again dont heat zinc/galv it will kill.
Dye such as gun bleu or gun brown or anodize almost any colour imaginable.
bead blaster makes a really nice finish on aluminum.
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