RED DEVIL "Lye" drain cleaner mixed with 3 gal. of water will give it a matte finish it only cost a few bucks. That will work on 6061 but if it is 2024 alloy or 7075 that has 5% copper in it will turn black then you have to desmut it. Desmut is a mixture of sulfuric and ferric acid.
These are all common acids that are used for DIY anodizing aluminum at home.
